Research

Interests: Carbohydrates; glycobiology; Golgi; membrane proteins; chemical biology

Glycosylation is the elephant in the room of biomedical research. Estimates suggest that more than 50 percent of eukaryotic proteins are glycosylated, and new forms of protein glycosylation are still being discovered. Glycosylation is also a common feature of lipids, with at least 200 distinct glycolipid structures known in eukaryotes. Unconjugated polysaccharide chains are also abundant and diverse in structure. About 2 percent of human genes are involved in carbohydrate metabolism and glycosylation. Individual differences in glycosylation may underlie much of human variation. Evolution has favored an emphasis on glycosylation; however, the modern research environment is less conducive to focusing on carbohydrate-containing molecules.

Unfortunately, many of the biochemical and analytical techniques that are used to study protein-protein interactions are poorly suited to the study of glycosylated molecules. First, glycan-mediated interactions are typically low affinity and do not survive the rigorous purification steps often used to identify binding partners. Second, protein-centric methods do not take into account the fact that glycosylated proteins typically exist as a mixture of glycoforms, each of which may have unique binding properties and activities. Finally, in many techniques (yeast two-hybrid, heterologous expression systems) the critical glycans are either absent on altered.

My research group at UT Southwestern is committed to developing and implementing new tools that are optimized for the study of glycosylated molecules. In particular, we invested significant effort in the development of photocrosslinking sugar analogs that can be metabolically incorporated into cellular glycoconjugates and used to covalently crosslink glycan-mediated interactions. These tools can now be deployed to study and identify transient glycan-mediated interactions. Our current research efforts are focused on two broad areas: (1) sialic acid-containing glycoconjugates (sialosides); and (2) O-GlcNAc-modified proteins. We are currently using photocrosslinking sialic acid analogs to study the interactions of sialic acid-interacting proteins, particularly those involved in infectious disease and cancer metastasis. We are using photocrosslinking GlcNAc to investigate the interactions of nucleoporins and other O-GlcNAc-modified proteins. In addition to our photocrosslinking studies, we have developed a new two-hybrid technique that can be used to interrogate protein-protein interactions in the Golgi and eukaryotic cells.

Research in the Kohler Lab is funded by the NIH (R01GM090271 and R21DK112733), the Welch Foundation (I-1686), and The Hartwell Foundation.