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. 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, we are studying the family of glucosaminyl 3-O-sulfotransferases (Hs3st) that modify heparan sulfate at rare sites and have developed genome-wide screening assays to look for novel genes involved in heparan sulfate formation.
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 and the non-reducing end of all glycosaminoglycan chains based on stable isotope tagging with aniline coupled with liquid chromatography-mass spectrometry. This highly sensitive technique has been developed into a diagnostic method for mucopolysaccharidoses and for monitoring therapy.