Aggrecan Glycosmioglycan Proteoglycan Degradation AGGRECAN GLYCOSYLATION AFFECTS CLEAVAGE BY AGGRECANASE

INTRODUCTION Cleavage of aggrecan within the interglobular domain (IGD) at the GluAla bond has been attributed to the protease “aggrecanase” (1,2). In addition to this cleavage site, aggrecanase has been shown to cleave within the C-terminal region of aggrecan between G2 and G3 (3). The core protein of aggrecan is highly glycosylated with regions rich in both keratan sulfate (KS) and chondroitin sulfate (CS). Since age-related changes in aggrecan glycosylation have been observed (4), these glycosaminoglycans (GAGs) may play a role in controlling aggrecan degradation. We had previously shown that although fully glycosylated aggrecan is readily cleaved by aggrecanase at the Glu-Ala bond, this cleavage is not observed when the aggrecan substrate is deglycosylated with chondroitinase ABC and keratanases prior to digestion (5). We have extended these observations by studying the individual roles of KS and CS in cleavage at the Glu-Ala bond, as well as at alternative aggrecanase cleavage sites within the Cterminal domain.