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Departments: Tenure-Track Faculty

Breeanna Urbanowicz

jennbryant on July 12, 2021

Short Biography:
Dr. Urbanowicz received her B.S. in Biology in 2001 from Purdue University and her Ph.D. in 2008 from Cornell University. Prior to her junior faculty position at the Complex Carbohydrate Research Center, Dr. Urbanowicz was a Postdoctoral Fellow (2008-2013) in the Department of Biochemistry and Molecular Biology at the University of Georgia.

Research Interests:
Biological molecules, including proteins, polysaccharides, and nucleic acids, are assembled to create complex structures with biochemical and biomechanical properties that are greater than the sum of their parts. My current research focuses on understanding the structure and function of plant carbohydrate active enzymes involved in polysaccharide biosynthesis and modification. Plant cell walls are complex macrostructures comprised of cellulose, hemicellulose, and pectins, together with lesser amounts of protein and phenolic molecules. These components assemble and interact with one another to produce dynamic structures with many capabilities, including providing mechanical support to plant structures and determining the size and shape of plant cells.
The research of my group focuses on understanding the integral steps in the molecular pathways used by plants to synthesize complex polysaccharides. A key area of interest is development of methods to express and analyze recombinant plant enzymes, which has allowed us to investigate plant biochemical pathways in vitro. We have now generated a large collection of recombinant enzymes that are able to catalyze highly specific, covalent modifications of polysaccharides, which we utilize as nature-inspired molecular tools for targeted functionalization and labeling of glycopolymers that greatly expand our toolkit for producing glycopolymer-based products with valuable properties.

• High throughput expression of plant biocatalysts. In collaboration with Kelley Moremen at the CCRC, we have designed and evaluated over 75 constructs for heterologous expression in HEK293 cells encoding plant glycosyltransferases (GTs) from diverse families in addition to both polysaccharide O-methyltransferases (O-MTs) and O-acetyltransferases (O-AcTs). Assessment of these constructs for both protein expression levels and retention of in vitro activity determined that this is a robust heterologous expression system for plant derived enzymes. We have applied this system to the in vitro synthesis of decorated hemicellulosic polymers, resulting in the first proof-of-concept generation of enzymatically synthesized, high degree of polymerization (DP), substituted plant polysaccharides in vitro (Urbanowicz et al., 2014).

• Polysaccharide Methyltransferases. We have shown that Arabidopsis GXMT1 encodes a glucuronoxylan (GX)-specific 4-O-methyltransferase responsible for methylating 75% of the GlcA residues in GX isolated from mature Arabidopsis inflorescence stems. Reduced methylation of GX in gxmt1-1 plants is correlated with altered lignin composition and increased release of GX by mild hydrothermal pretreatment (Urbanowicz et al., 2012). The ability to selectively manipulate polysaccharide O-methylation may provide new opportunities to modulate biopolymer interactions in the plant cell wall. We are currently investigating the role of other members in this family on polysaccharide methyletherfication.

• Investigating the mechanism of polysaccharide O-acetylation. Despite the high degree of O-acetyl substituents found in plant glycopolymers, the biochemical and mechanisms of polysaccharide O-acetylation employed by plants are still lacking. An unsolved question is the source of the acetyl group used by acetyltransferases. We have developed robust methods to biochemically analyze O-acetyltransferases and are applying these techniques to investigate the molecular details of polysaccharide methylation.

Michael Tiemeyer

jennbryant on July 12, 2021

Short Biography:
Dr. Tiemeyer received his B.A. in biology in 1982 and his Ph.D. in neuroscience in 1989 from The Johns Hopkins University. He was a Helen Hay Whitney postdoctoral fellow in developmental neurobiology at the University of California at Berkeley. Prior to joining the CCRC faculty, Dr. Tiemeyer was a faculty member in cell biology at Yale University School of Medicine and Director of Biochemical and Clinical Analytics and New Methods Development at Glyko/Biomarin, Inc. Full publications: 27.

Research Interests:
The surfaces of all eukaryotic cells are richly endowed with a diverse array of complex glycoconjugates. Therefore, carbohydrate moieties linked to protein, lipid, and glycosaminoglycan form the interfaces at which cell-cell interactions occur. Consistent with their subcellular location and structural diversity, specific oligosaccharides function as cell-surface tags that allow cells to appropriately interact with each other and with their local environment. In fact, cell surface carbohydrates are among the most discriminating markers for cellular differentiation and pathogenesis. We utilize genetic, molecular, and chemical techniques in vertebrate (mouse) and insect (Drosophila) model systems to study two aspects of carbohydrate expression. First, we investigate the influence of cell surface carbohydrates on development of the nervous system. We identified and characterized a novel carbohydrate binding protein (Gliolectin) that mediates the fidelity of axon pathfinding early in neural development. Second, we study mechanisms that control tissue- and stage-specific oligosaccharide expression. We discovered that a member of the Toll-like receptor family (Tollo) influences tissue-specific glycosylation through cell-cell communication. Our results have implications for facilitating regeneration of axon pathways in the nervous system, for understanding innate immunity and tissue surveillance, and for controlling the cellular changes that precede tumor metastasis.

Christine Szymanski

jennbryant on July 12, 2021

Short Biography:

Dr. Szymanski has been exploring bacterial glycomics for three decades, working on food pathogens since the early 1990s, with a particular emphasis on Campylobacter jejuni. She combines her expertise in food safety and animal health with novel therapeutic diagnostic platforms developed during her postdoctoral fellowship at the Naval Medical Research Center vaccine program (1996-2000), the key findings while employed at the National Research Council of Canada (2000-2008), and the translational advances during her tenure as an Alberta Innovates Technology Futures Scholar at the University of Alberta (2008-2016). She was the first to demonstrate that bacteria are capable of N-glycosylating proteins and is now exploiting these systems to create glycoconjugate vaccines and oral therapeutics through recombinant expression in Escherichia coli. Dr. Szymanski was also the first to demonstrate that viruses specific for bacteria express proteins that can be used as novel therapeutics in addition to their recognized diagnostic value. These viruses (bacteriophages) are the most abundant biological entity on earth (10+31) and are therefore a limitless resource for exploitation, especially in the area of glycomics.

Research Interests:

The Szymanski laboratory is a microbial glycobiology laboratory using multidisciplinary techniques and relevant model systems to: 1) characterize bacterial glycoconjugate pathways, 2) exploit bacteriophage recognition proteins that bind these structures, and 3) understand the protective benefits of host milk oligosaccharides to develop novel therapeutics and vaccines for the prevention of diarrheal diseases and post-infectious neuropathies such as Guillain-Barré Syndrome. These studies have also expanded our knowledge of carbohydrate metabolism by the gut microbiota and the transfer of antibiotic resistance between bacteria.

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James Prestegard

jennbryant on July 12, 2021

Short Biography:
Dr. Prestegard received his B.S. in chemistry in 1966 from the University of Minnesota and his Ph.D. in chemistry from the California Institute of Technology in 1971. Prior to joining the CCRC in January 1998, Dr. Prestegard spent 27 years in the Chemistry Department at Yale University where he held positions of assistant professor, associate professor, and professor. In addition to his normal professorial duties, he now directs the regional NMR facilities at the University of Georgia. Dr. Prestegard serves on the editorial boards of several journals, including the Journal of Magnetic Resonance and the Journal of Biomolecular NMR, and is a frequent member of advisory and review panels.

Research Interests:
Dr. Prestegard’s group is applying nuclear magnetic resonance (NMR) spectroscopy to the study of the structure and function of biologically important macromolecular assemblies involving carbohydrates, proteins, and membranes. Research in the Prestegard laboratory focuses on NMR methods development, membrane proteins, cell-surface carbohydrates, protein structure, and protein-protein interactions.

Proteins are large molecules that are targets (receptors) of natural ligands (smaller molecules that bind specifically to the active site of a protein) as well as pharmaceuticals. An essential part of developing any new drug is to determine how that drug will bind to its target protein(s) and to characterize the structures and conformations of the interacting molecules, a particularly difficult task when flexible structures such as carbohydrates are involved. Nuclear magnetic resonance (NMR) spectroscopy is rapidly becoming a major contributor of structural information on how natural ligands and derived drug candidates bind to protein targets. However, progress has been impeded by reliance on short-range interactions (known as NOEs) that are limited in their ability to characterize the relative placement of remote parts of macromolecules or to characterize the average conformation of flexible ligands. These limitations are particularly severe in recognition of carbohydrate-containing ligands because they are inherently flexible and because the proteins that recognize them often function as multimers of loosely connected domains.

The Prestegard group has recently made some important advances in developing non-NOE-based structure determination methods. These methods rely on a more direct NMR measurement that can be made in “ordered” media, in the presence of high magnetic fields. Using these new methods the Prestegard group has succeeded in characterizing the relative orientation of two domains in a carbohydrate-binding protein and in collecting structural data on a flexible trisaccharide (a molecule composed of three sugars) without the use of NOEs. The experiments provide data in a fraction of the time required by the traditional NOE-based approach and can provide a unique structural perspective on which to base the design of new drugs.

NMR methods development. Methods development is closely related to the demands of the applications. For example, some exciting diffusion-edited amide exchange experiments have been developed for the investigation of the energetics and kinetics of protons involved in hydrogen bonds. Hydrogen bonding is important in stabilizing protein structural elements and in protein-carbohydrate recognition, both subjects being studied in the Prestegard group. Neural network-based automated assignment programs for multi-dimensional NMR spectra have been developed, as have statistics-based spectral analysis programs. These programs are essential in achieving less tedious and more precise NMR-based structural analysis.

An ongoing objective of the Prestegard group is to extract new types of information from NMR and related experiments. Current projects involve the use of residual dipolar couplings that occur in molecules oriented by very high magnetic fields and cross-correlation effects that involve chemical shift anisotropies that also become large in high fields. Both topics rely on the design of new experiments and in-depth theoretical analysis of experimental results.

Membrane proteins. The structural analysis of membrane proteins is one of the major challenges in biophysical chemistry today. It is a major challenge because these proteins prefer an environment that is neither crystal nor solution. Unfortunately, crystal and solution phases are the only two phases for which structure determination methods are well established. The Prestegard lab has undertaken the development of NMR-based structure determination methods that are applicable in a medium that mimics the partial, liquid crytalline order of natural membranes. These methods are currently being applied to peptides that present typical membrane protein structural motifs, such as trans bilayer helices and surface-associated amphipathic helices.

Cell-surface carbohydrates. Carbohydrates covalently linked to proteins (glycoproteins) and to lipids (glycolipids) are also present on the surfaces of membranes. In fact, they are the primary mediators in processes that involve interaction of a cell with its external environment. This external environment includes important processes such as cell-cell interactions, hormone stimulation, and invasion by pathogens. Structural characterization of the carbohydrate moieties in their nature environment is essential to understanding and controlling the processes in which they are involved. Many of the NMR methods being developed to characterize membrane proteins are equally applicable to cell-surface carbohydrates. In addition, methods that are more focused on the details of protein-carbohydrate recognition interactions are important. A number of lectins from plant and animal sources are being studied as models for these recognition processes and as a testing ground for methods that can characterize them.

Protein structure and protein-protein interactions. Knowledge of protein structure is essential to understanding a very large number of biochemical processes. However, proteins seldom act alone. They interact with substrates, receptors, and one another to fine tune their activities and specificities. NMR spectroscopy offers the opportunity not only to determine protein structure (in solution, for the cases of interest to the Prestegard group) but to focus on particular regions involved in critical contacts. Isotope-edited NMR experiments are a key component enabling analyses of these special regions. The Prestegard group has implemented a full array of these experiments and is applying them to interesting protein systems. One study involves components of chaperonin systems important to protein folding. Another involves components of multi-enzyme systems important in the synthesis and modification of long chain fatty acids.

Dr. Prestegard’s research is supported by the National Science Foundation, the National Institutes of Health, and the Georgia Research Alliance.

Michael Pierce

jennbryant on July 12, 2021

Short Biography:
Dr. Pierce received his Ph.D. in biology in 1980 from the Johns Hopkins University. Prior to joining the CCRC in April 1991, Dr. Pierce was assistant then associate professor in the Department of Cell Biology and Anatomy at the University of Miami School of Medicine and Staff Investigator of the Papanicolau Comprehensive Cancer Center. In 1988 he was the recipient of a five-year Faculty Research Award from the American Cancer Society. He now serves on the editorial boards of the Journal of Biological Chemistry and Glycobiology. He now serves as Co-Chair of the Alliance for Glycobiologists for Cancer Detection, the Cancer Biology Chair of the Consortium for Functional Glycomics, and 2015 President of the Society for Glycobiology. He is P.I. of the NIGMS National Center for Biomedical Glycomics and Co-P.I. of the NIH Glycoscience Predoctoral Training Program (GTP). His funding comes from NIGMS and NCI.

Research Interests:
Glycan structures change during oncogenesis; these changes are often hallmarks of cancer progression. Our lab investigates:
What are the precise glycan structural changes that occur?
How these changes are regulated at the molecular level?
What are the functional consequences of these changes?
Can these changes be exploited to develop potential diagnostics or therapeutics?
We isolated a cDNA encoding a glycosyltransferase whose activity and product is increased in many cancers, particularly epithelial-derived and showed that its transcript was upregulated via the ras-raf-ets oncogenic signaling pathway.
Our main focus now is on a unique N-glycan whose expression is only on a few proteins in the human genome (protein-site-specific) and appears to be an excellent marker for pancreatic carcinoma.
Discovery of a novel family of innate immune lectins

The X-lectin family is found in deuterostomes from the sea cucumber to man
Over 240 sequences from lectins in this family are now in the database
We isolated the Xenopus laevis cortical granule lectin and with Kelley Moremen showed that it had two human homologs
These human homologs, the intelectins, are constitutively expressed in various endothelial cells, Paneth cells, and are induced in respiratory and intestinal epithelia by IL-13, an innate immune cytokine produced by immune cells
Recent results show intelectin-1 binds and kills specific pathogenic bacteria
We are defining the specificities of the binding sites on various intelectins and working to discover their structures and functions
Here is a recent seminar that I presented as part of the Goldstein Lectureship, University of Michigan Department of Biochemistry and Molecular Biology.

Ron Orlando

jennbryant on July 12, 2021

Short Biography:
Dr. Orlando received his B.S. in natural science in 1983 from St. Mary’s College of Maryland and his Ph.D. in analytical chemistry in 1988 from the University of Delaware. He joined the CCRC in January 1993. He heads the CCRC’s mass spectrometry facility and was named a “Leader of Tomorrow” in 1995 by the journal Spectroscopy. In 1996 he was invited by the journal Analytical Chemistry to review the MS calculator Softshell. He has two U.S. patent applications pending. Dr. Orlando is a frequently invited seminar speaker at international colloquia and at research institutes, academic departments, and industrial organizations around the world. He was invited by the ACS Divisions of Analytical and Carbohydrate Chemistry to organize a session entitled, “Advances in Mass Spectrometry of Carbohydrates” at the 211th National Meeting of the American Chemical Society in March 1996 and chaired a session entitled, “Mass Spectrometry in the 21st Century” at the SUNBOR 50th Anniversary Symposium in Osaka, Japan, in June 1996. Full publications: 50.

Research Interests:
Dr. Orlando conducts research on using mass spectrometry (MS) to answer biological questions. He also is concerned with developing new methodologies to increase the amount of information obtained from MS experiments and to reduce the quantity of material needed for analysis. The procedures Dr. Orlando and his group have developed can currently elucidate the complete primary structures of the carbohydrate side chains of glycoproteins (including the stereochemistry, linkage, and anomeric configuration of each monosaccharide) from only low picomole quantities of sample.
The carbohydrate side chains of enzymatically glycosylated proteins play important, often essential, roles in the functions of glycoproteins. Carbohydrates linked through asparagine residues (N-linked) of glycoproteins participate in such health-related processes as hormone action, cancer, viral infection, and cell development and differentiation. The biological functions of carbohydrate chains attached through serine or threonine residues (O-linked) of glycoproteins are less well-defined, although these carbohydrate chains appear to be required for the biosynthesis, secretion, and compartmentalization of some glycoproteins. Alternatively, the non-enzymatic glycosylation (glycation) of proteins is believed to disrupt the normal structure and function of proteins and has been implicated in a range of health problems, particularly those associated with diabetes such as the development of cataracts.

The structural characterization of complex biologically active glycoproteins, essential to understanding their biological functions, currently holds numerous challenges for the biomedical researcher. Biomedically relevant glycoproteins typically can only be isolated in picomole quantities, while many of the techniques available for structurally analyzing the carbohydrate chains require at least nanomole quantities of material. Furthermore, no generally applicable strategy has been developed to determine O-linked glycosylation sites. The most widely used techniques for studying the carbohydrate portions of glycoproteins incorporate chemical or enzymatic release of the carbohydrate side chains from the peptide backbone prior to their structural analysis. However, the separation of the carbohydrate side chains from the peptide means that the point of attachment for each carbohydrate chain and the carbohydrate heterogeneity at each glycosylation site cannot be determined.

Dr. Orlando and his group are involved in several research projects that will continue their development of new MS strategies to structurally characterize glycoproteins. This work focuses on analyzing glycopeptides prior to removal of their carbohydrate side chains and reducing the sample quantities required for these MS procedures. Currently, they can characterize the complete primary structure of a glycoprotein from only 1-10 picomole of sample, approximately 5,000 times less material than is needed for present conventional methods. This work is also expected to produce general schemes for analyses that are particularly challenging for existing methodology, such as determining O-linked glycosylation and/or glycation sites. As new techniques are developed and refined, they are used to structurally characterize biologically significant glycated and glycosylated proteins.

For example, the discovery of elevated levels of glycated albumins and hemoglobins in diabetic patients has focused attention on the roles played by glycation in a range of health-related problems. Glycation is prevalent in diabetics in particular because of the frequent occurrence of high blood sugar levels in these patients. This modification of protein chains results from the irreversible addition of a saccharide to the free amino groups of lysines or the N-terminus of a protein. However, the lack of sensitive analytical procedures to structurally characterize glycated proteins has limited most research in this area to those glycated proteins that are easily obtained in large quantities, rather than to being able to study the effects of glycation in critical biomedical processes. Glycation of difficult-to-obtain proteins, therefore, may be responsible for a number of health-related problems in diabetics, including the development of cataracts. Glycation is believed to play a role in cataract development because it purportedly disrupts the structure of the eye lens proteins (crystallins). The tight, stable packing of the crystallins provides the optical characteristics necessary for vision. When this packing is disrupted by glycation, the refractive index of the lens is altered, causing light scattering and eventual lens opacity (cataracts).

Dr. Orlando’s group is investigating the structural characterization of crystallins obtained from human eye lenses of healthy and diabetic patients. A major goal of this investigation is to determine the extent of crystallin glycation and the sites of sugar attachment in the crystallins of diabetic patients as compared to healthy individuals to learn more about the role of glycation in cataract development. The techniques developed during the study of glycated crystallins are expected to open up new areas of investigation concerning the role of glycation in other health-related problems associated with diabetes, such as kidney dysfunction, osteoporosis, and osteopenia. Dr. Orlando’s work is supported by the National Institutes of Health, the National Science Foundation, and industrial sources.

Kelley Moremen

jennbryant on July 12, 2021

Short Biography:

Dr. Moremen received his B.S. in Biology and Chemistry (1978) from Dickinson College and his Ph.D. in Molecular Biology (1984) from Vanderbilt University. Prior to joining the faculty at the CCRC in 1991, he spent five years as a Postdoctoral Fellow at Massachusetts Institute of Technology. Dr. Moremen has served as chair of the Glycobiology Gordon Research Conference, President, Board of Directors, and Secretary of the Society for Glycobiology. He directed efforts on an NIH funded multi-investigator ‘Resource for Integrated Glycotechnology’, served as a senior investigator on the NIH-funded ‘National Center for Biomedical Glycomics’, and is a lead Principal Investigator or Senior Investigator on eight additional grants from the NIH and Department of Energy. In 2018 he launched a biotech startup, Glyco Expression Technologies, Inc., as a part of the UGA Innovation Gateway. He has served on editorial boards of Journal of Biological Chemistry, Glycobiology, and Glycoconjugate Journal, numerous NIH grant review panels, and Scientific Advisory Boards of four biotech companies. In 2014 Dr. Moremen was appointed the Distinguished Research Professorship in Biochemistry and Molecular Biology at the University of Georgia and in 202 was awarded the Karl Meyer Lectureship from the Society for Glycobiology. Dr. Moremen has 10 patents and over 180 publications.

Research Interests:

Research in the Moremen lab focuses on the biochemistry, structure, and regulation of enzymes involved in the biosynthesis, recognition, and catabolism of mammalian glycoproteins. Carbohydrate structures on glycoproteins contribute to many biological recognition events during development, oncogenic transformation, and cell adhesion. Large numbers of intracellular and extracellular proteins contain covalently bound glycans and alterations in the synthesis and degradation of these structures can occur in human genetic diseases and cancer. Many questions remain regarding the regulation of glycosylation pathways, the structures and functions of the processing enzymes, and the specificity and regulation of protein-carbohydrate interactions during development. Research in the Moremen lab is focused on developing novel strategies to address contemporary problems in the regulation, roles, mechanism, and machinery of mammalian protein glycosylation with efforts in four main areas:

1) Structures, specificities and mechanisms of mammalian glycosylation enzymes: Studies on the mammalian glycosylation enzymes in the Moremen lab have expanded in recent years with the development of a unified design and expression platform (Repository of Glycan-related Expression Constructs) for recombinant production of all mammalian glycosyltransferases, glycosidases, and sulfotransferases (target gene list of >400 coding regions) in bacteria, baculovirus, and mammalian cells. This multi-investigator effort, initiated and coordinated within the Moremen lab, is focused on production of these recombinant enzymes and has led to new enzyme structures and insights into the structural basis for enzymatic glycan synthesis. This project has led to numerous additional applications in chemoenzymatic synthesis, biochemical and structural studies, and development of technologies for enzymatic modification of glycoproteins and glycolipids in cellular environments to monitor molecule redistribution in the course of disease. The goals of these studies are to provide a biochemical and structural understanding of glycan biosynthesis and catabolism as well as providing enzymatic catalysts for chemoenzymatic synthesis. This project has been funded by an NIH P01 grant (P01GM107012, Mammalian Glycosyltransferases for Use in Chemistry and Biology) and presently by a multi-investigator NIH R01 grant (R01GM130915, Origin of N-Glycan Site-Specific Heterogeneity). For further information please see: glycoenzymes.ccrc.uga.edu.

2) Protein-carbohydrate interactions: Cell-surface and extracellular glycoproteins and glycolipids play unique and critical roles in mammalian physiology. One of the major glycan classes at the cell surface and within the extracellular matrix are the proteoglycans (PGs) that play diverse roles as co-receptors for cell surface signaling, scaffolds for cell-matrix interactions, ligands that create morphogen or chemokine gradients in development and inflammation, and numerous other contributions to signaling and cell surface structure. Little is known about the details of PG interactions with binding partners or their mechanisms of biological function. The Moremen lab directs a multi-investigator project with goals to develop a novel, integrated technologies that will address the challenges of PG structures, interactions, and biological functions by leveraging advances in analytical, synthetic, structural, biochemical and biological tools. This project has been funded by an NIH P41 grant (P41GM103390, Resource for Integrated Glycotechnology). For further information please see: glycotech.uga.edu.

3) Regulation of glycosylation machinery in mammalian systems: The Moremen lab is also involved in a collaborative project focused on determining the structures and regulation of glycans associated with glycoproteins and glycolipids in animal systems. The overall aims of the program are to examine the changes glycan structures during development with a particular focus on embryonic stem cell differentiation. The Moremen lab has developed platforms for analysis of glyco-gene transcript abundance using a custom real-time RT-PCR strategy as well as next-generation RNA-Seq methods. Integration of the transcript abundance data with the glycan structure analysis developed by other research groups in the CCRC will be accomplished through the bioinformatics group associated with the research program. This project has been funded by an NIH P41 grant (P41GM103490, National Center for Biomedical Glycomics). For further information please see: glycomics.uga.edu

4) Structure and biochemistry of glycan trimming enzymes involved in glycoprotein biosynthesis and catabolism: The fourth area of focus in the Moremen lab is on the enzymes involved in glycan trimming in the secretory pathway that are essential for N-glycan maturation as well as playing a role in the catabolism of misfolded nascent glycoproteins in the endoplasmic reticulum (ER-associated degradation).

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Debra Mohnen

jennbryant on July 12, 2021

Short Biography:

Debra Mohnen is a Distinguished Research Professor at the Complex Carbohydrate Research Center, as well as the Department of Biochemistry and Molecular Biology at the University of Georgia. Dr. Mohnen received her B.A. in Biology (1979) at Lawrence University, Appleton, WI and her M.S. in Botany (1981) and Ph.D. in Plant Biology (1985) from the University of Illinois, Urbana, IL, with research conducted at the Friedrich Miescher Institute, Basel, Switzerland. Prior to joining the CCRC, she carried out five years of postdoctoral research at the CCRC and USDA, ARS, Russell Research Center in Athens, Georgia. Dr. Mohnen has served as Chair of the Plant Cell Wall Gordon Conference and since 1990 has lead a research team focusing on pectin synthesis, structure and function, with emphasis on the role of pectin glycan domains in wall architecture and plant cell growth. In 2008 she was awarded the Bruce Stone Award for research in pectin synthesis and elected as a fellow of the American Association for the Advancement of Science in 2013. Her research on synthesis of the two pectin glycan backbones, homogalacturonan and rhamnogalacturonan, led to the discovery of the GAUT and RGGAT families of glycosyltransferases and the recognition that pectin exists and functions as a family of glycan domains in cell wall heteroglycans and glycoconjugates. Since 2007 part of her research has been directed at improving plant biomass yield, sustainability and composition for the production of biofuel and biomaterials. As Focus Area Lead of Plant Biomass Formation and Modification in the DOE-funded BioEnergy Science Center (BESC), she directed a team of researchers aimed at understanding and overcoming biomass recalcitrance to deconstruction and since 2017 she serves as Research Domain Lead for Integrative Analysis and Understanding in the Center for Bioenergy Innovation (CBI). Her current efforts are focused on a new model for pectin function in cell expansion and wall structure. 

Research Interests:
Dr. Mohnen’s research focuses on the biosynthesis, function and structure of plant cell wall polysaccharides and glycoconjugates, with emphasis on pectin, matrix polysaccharides and wall proteoglycans.

The research goals include:

*Understanding the structure, biosynthesis and function of wall polymers that contain pectic glycans.

*Improving plant growth and development, and the use and conversion of plant cell wall biomass to biofuels and bioproducts, through modification of wall structure and synthesis.

*Reevaluation of plant cell wall models based on recently identified wall matrix glycan-containing proteoglycan structures, and glycosyltransferase gene family member functionalities, that are inconsistent with current wall models.

The research includes biochemical, chemical, molecular genetic and genomic methods and use of both model systems (e.g. Arabidopsis and rice) and biomass feedstock (e.g. Populus and switchgrass).

Robert Haltiwanger

jennbryant on July 12, 2021

Short Biography:
Dr. Haltiwanger received his B.S. in Biology (1980) and Ph.D. in Biochemistry (1986) from Duke University. He went on to do postdoctoral work at Johns Hopkins University School of Medicine, and took his first independent position as an Assistant Professor in the Department of Biochemistry and Cell Biology at Stony Brook University (1991). He rose through the ranks to full Professor and served as Chair of that Department for 8 years. He moved to the CCRC in 2015 as the GRA Eminent Scholar in Biomedical Glycosciences. He has served as President of the Society for Glycobiology, Chair of the Glycobiology Gordon Conference, and currently serves as Editor-in-Chief of the journal Glycobiology.

Research Interests:
Glycobiology is a relatively young field that focuses on examining the biological effects of modifying proteins and lipids with carbohydrates. Glycans provide incredible structural diversity to biological systems, offering the potential to alter function in a wide variety of ways, but also bringing significant technical challenges for structural analysis. Advances in methodologies to examine these structures has brought significant insight into functions for glycans in a wide variety of biological contexts over the past decade, causing rapid growth and interest in the field. My laboratory focuses on the role of carbohydrate modifications on proteins, especially as they affect cellular communication events. Protein glycosylation exists in two major forms: N-linked, referring to glycans linked to protein through the amide nitrogen of asparagine residues, and O-linked, where the glycans are linked through the hydroxyl groups of serine or threonine. O-Glycans are divided into subclasses based on the carbohydrate linked directly to the serine or threonine. The subclasses that we focus on are called O-fucose and O-glucose. All of the projects in the laboratory deal with learning more about these forms of glycosylation. Several are discussed in more detail below.

Regulation of Notch Signaling by O-fucose and O-glucose:

The Notch protein plays a key role in communication between cells. It functions at the surface of the cell where it binds to ligands expressed on adjacent cells (e.g. Delta, Serrate, Jagged), resulting in its activation. Such communication between cells is essential for proper development of metazoans, and defects in Notch function result in a number of human diseases, including severe mental and physical retardation, congenital heart defects, vascular defects leading to stroke and dementia, and several forms of cancer. A clear understanding of how Notch functions is essential to develop therapies for these diseases.

We have demonstrated that O-fucose and O-glucose glycans modify the Epidermal Growth Factor-like (EGF) repeats of the Notch extracellular domain. We have identified the enzymes responsible for addition of the O-fucose, protein O-fucosyltransferase 1 (POFUT1) and O-glucose, protein O-glucosyltransferase 1 (POGLUT1) to Notch. Elimation of either of these enzymes in mice or flies results in severe Notch phenotypes. Thus, the O-fucose and O-glucose modifications are essential for proper Notch function. Several studies suggest that the O-fucose modifications are important for Notch to be able to bind to its ligands. O-Glucose modifications do not affect ligand binding so affect Notch function through some other mechanism. We are currently investigating in molecular detail how O-fucose and O-glucose affect Notch.

Both O-fucose and O-glucose are elongated by other sugars, and this elongation regulates Notch activity. We have demonstrated that the Fringe protein is a glycosyltransferase that adds an N-acetylglucosamine (GlcNAc), to O-fucose on Notch. Fringe modification modulates Notch function, increasing and/or decreasing its response to ligands depending on the circumstances. These results demonstrated that cellular communication through the Notch protein can be regulated by altering the carbohydrate structures (O-fucose structures) on Notch. This was a very important finding for the field of Glycobiology, as it was a clear example of a principle proposed over 50 years ago, that carbohydrate modifications on cell surface receptors could modulate their function. We know that Fringe-mediated changes in O-fucose structures alter Notch-ligand binding, and we are examining at a molecular level how this occurs.

O-Glucose is elongated by xylose residues, and in collaboration with Dr. Hamed Jafar-Nejad’s group we have shown that elongation of O-glucose inhibits Notch activity. We are currently examining the molecular mechanisms for how O-glucose modifications affect Notch activity.

O-fucose modifications on Thrombospondin Type 1 Repeats:

O-Fucose modifications also exist in a different protein context called a thrombospondin type 1 repeat (TSR). TSRs are found in dozens of cell-surface and secreted proteins, and most are predicted to be modified with O-fucose. We have identified the enzyme responsible for adding O-fucose to TSRs, protein O-fucosyltransferase 2 (POFUT2), a distant homolog of POFUT1. Elimination of POFUT2 in mice results in embryonic lethality just after gastrulation. We are currently examining which POFUT2 targets are responsible for this lethality.

We have also identified the enzyme that adds a glucose residue to the O-fucose on TSRs to generate a Glucose-β1,3-Fucose disaccharide called β3-glucosyltransferase (B3GLCT). Mutations in B3GLCT result in a rare developmental disorder known as Peter’s Plus Syndrome (PPS). PPS patients display a number of developmental abnormalities including eye defects, short stature, brachydactyly, cleft palate, and unusual craniofacial features. Our recent studies suggest that both POFUT2 and B3GLCT are required for proper folding of TSRs. Thus, loss of either enzyme causes folding defects in proteins containing TSRs. We are currently pursuing how addition of these sugars affects the folding of the TSRs.

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Michael G Hahn

jennbryant on July 12, 2021

Short Biography:
Dr. Hahn received a B.S. in chemistry and a B.A. in Independent Studies in 1974 from the University of Oregon and his Ph.D. in biochemistry in 1981 from the University of Colorado. A postdoctoral research associate appointment at the University of Wisconsin-Madison in plant pathology followed, after which Dr. Hahn went to the Albert-Ludwigs-Universiät (Freiburg, Germany) with the support of an Alexander-von-Humboldt stipend. Following another postdoctoral research associate appointment at the Salk Institute (San Diego, CA), Dr. Hahn joined the CCRC in July 1986. Full publications: 77.

Research Interests:
Our laboratory studies the cell biology and biosynthesis of plant cell walls. Plant cell walls play major roles in the biology of plants. Examples of these roles include controlling the growth and shape of plant cells, tissues, organs, and ultimately the entire plant, regulating the movement of nutrients and signals within the apoplast and toward the plasma membrane, serving as the first line of defense against pathogens and environmental stresses, and acting as a source of signaling molecules important in plant development and defense. Plant cell walls are also the principal component of plant biomass, which has become a focal point in the search for alternative and renewable sources of energy (biofuels).
We are pursuing two broad research goals:

(A) We are investigating plant cell wall biosynthesis by looking at two families of genes, primarily in Arabidopsis, thought to encode glycosyltransferases involved in plant cell wall glycan biosynthesis: 1) GAlacturonosylTransferase-Like (GATL) proteins thought to be involved in pectin biosynthesis; 2) FUcosylTransferase (FUT) proteins thought to add fucosyl residues to diverse plant cell wall glycans.

(B) We have developed a large and diverse library of monoclonal antibodies against plant cell wall glycans. These antibodies are being used to determine the locations of diverse cell wall carbohydrate structures (epitopes) in Arabidopsis, switchgrass and poplar. These antibodies are also proving useful for plant cell wall mutant characterization studies, and for quantitating glycans in cell wall extracts.

Our laboratory utilizes a broad range of experimental approaches in these studies, including molecular genetic, biochemical, immunological and microscopic techniques.

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