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 have a genome wide CRISPR-Cas9 screening underway to look for novel genes involved in assembly. Other studies focus on identifying components of the GAGosome, a complex of enzymes and regulatory factors in the Golgi. We are also interested in lysosomal catabolism of glycosaminoglycans and have an ongoing project focused on pathological changes that take place when degradation is genetically altered.
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.
Kowalewskia, B., Lamanna. W.C., Lawrence, R., Dammea,M., Stroobantsc, S., Padvad, M., Kalusa, I., Fresea, M.A., Lübkea, T., Lüllmann-Rauche, R., D’Hoogec, R., Esko, J.D., and Dierk, T. (2012) Arylsulfatase G inactivation causes loss of heparan sulfate 3-O-sulfatase activity and mucopolysaccharidosis in mice. Proc. Natl. Acad. Sci. USA 109:10310-10315
Wen, J., Xiao, J., Rahdar, M., Choudhury, B.P., Cui, J., Taylor, G.S., Esko, J.D., and Dixon, J.E. (2014) Xylose phosphorylation functions as a molecular switch to regulate proteoglycan biosynthesis. Proc. Natl. Acad. Sci. USA 111:15723-8.
Lawrence, R., Brown, J.R., Lorey, F., Dickson, P.I., Crawford, B.E., and Esko, J.D. (2014) Glycan-based biomarkers for mucopolysaccharidoses. Molec. Gene. Metabolism 111:73-83
Dhamale, O.P., Lawrence, R., Wiegmann, E.M., Shah, B.A., Al-Mafraji, K., Lamanna, W.C., Lübke, T., Dierks, T., Boons, G.-J. and Esko, J.D. (2017) Arylsulfatase K is the lysosomal 2-sulfoglucuronate sulfatase.ACS Chem. Biol. In press.
Dwyer, C.A., Scudder, S.L., Lin, Y., Dozier, L.E., Phan, D. Allen, N.J., Patrick, G.N. and Esko, J.D. (2017) Neurodevelopmental changes in excitatory synaptic structure and function in the cerebral cortex of Sanfilippo Syndrome IIIA mice. Sci. Rep., submitted.