Posttranslational modifications of microfibril associated glycoprotein-1 (MAGP-1)

Microfibril-associated glycoprotein-1 (MAGP-1) is a small molecular weight protein associated with extracellular matrix microfibrils. Biochemical stud ies have shown that MAGP-1 undergoes several posttranslational modification s that may influence its associations with other microfibrillar components. To identify the sites in the molecule where posttranslational modification s occur, we expressed MAGP-1 constructs containing various point mutations as well as front and back half truncations in CHO cells. Characterization o f transiently expressed protein showed that MAGP-1 undergoes O-linked glyco sylation and tyrosine sulfation at sites in its amino-terminal half. This r egion of the protein also served as a major amine acceptor site for transgl utaminase and mediated self-assembly into high molecular weight multimers t hrough a glutamine-rich sequence. Fine mapping of the modification sites th rough mutational analysis demonstrated that Gln20 is a major amine acceptor site for the transglutaminase reaction and confirmed that a canonical tyro sine sulfation consensus sequence is the site of MAGP-1 sulfation. Our resu lts also show that O-glycosylation occurs at more than one site in the mole cule.