Proteoglycan Metabolism
Virtually all animal cells carry proteoglycans on their plasma membrane and secrete them into the surrounding extracellular matrix. Proteoglycans consist of a protein core and one or more glycosaminoglycan chains, such as heparan sulfate (which is related in structure to the anticoagulant heparin) or chondroitin sulfate/dermatan sulfate. During their biosynthesis, a large family of enzymes install sulfate groups at various positions along the chains, creating binding sites for ligands, such as growth factors, proteases and their inhibitors, lipolytic enzymes and plasma apolipoproteins, and extracellular matrix proteins. The importance of these interactions is exemplified by the profound pathophysiological phenotypes in mice and humans bearing mutations in the core proteins or the biosynthetic enzymes responsible for assembly of the chains.
Ongoing projects include creation of conditional mutants in mice in order to study the function of heparan sulfate and chondroitin sulfate proteoglycans in different physiological systems (see other pages on this website). We are also interested in the process of assembly, in particular how cells regulate the formation of ligand binding sites in the chains. Towards this end, two families of enzymes are under study, the GlcNAc N-deacetylase/N-sulfotransferases (Ndst) and the glucosaminyl 3-O-sulfotransferases (Hs3st) that modify heparan sulfate.
A challenge in this field is the development of techniques to analyze the structure of the glycosaminoglycan chains. We developed a highly sensitive method for analyzing the disaccharide subunit structure of all glycosaminoglycan chains based on stable isotope tagging with aniline coupled with liquid chromatography-mass spectrometry. This highly sensitive technique can be used to study how the enzymes regulate the pattern of sulfation of the chains and has already led to the discovery of unusual modifications in lower organisms.
Relevant Papers
Bishop, J.R., Schuksz, M., and Esko, J.D. (2007), Heparan sulfate proteoglycans fine-tune mammalian physiology. Nature 446:1030-1037.
Lawrence, R., Olson, S.K., Steele, R.E., Wang, L., Zhang, L., Warrior, R., Cummings, R.D. and Esko, J.D. (2008) Evolutionary differences in glycosaminoglycan fine structure detected by quantitative glycan reductive isotope labels. J. Biol. Chem., in press.
Lawrence, R., Lu, H., Rosenberg, R.D., Esko, J.D., Zhang, L. (2008) Disaccharide structure code for the easy representation of constituent oligosaccharides from glycosaminoglycans. Nat. Methods. 5:291-292