PRIMARY STRUCTURE AND EXPRESSION OF MATRILIN-2, THE CLOSEST RELATIVE OF CARTILAGE MATRIX PROTEIN WITHIN THE VON-WILLEBRAND-FACTOR TYPE A-LIKE MODULE SUPERFAMILY

A mouse cDNA encoding a novel member of the von Willebrand factor type A-like module superfamily was cloned, The protein precursor of 956 am ino acids consists of a putative signal peptide, two von Willebrand fa ctor type A-like domains connected by 10 epidermal growth factor-like modules, a potential oligomerization domain, and a unique segment, and it contains potential N-glycosylation sites, A sequence similarity se arch indicated the closest relation to the trimeric cartilage matrix p rotein (CMP), Since they constitute a novel protein family, we introdu ce the term matrilin-2 for the new protein, reserving matrilin-1 as an alternative name for CMP. A 3.9-kilobase matrilin-2 mRNA was detected in a variety of mouse organs, including calvaria, uterus, heart, and brain, as well as fibroblast and osteoblast cell lines, Expressed huma n and rat cDNA sequence tags indicate a high degree of interspecies co nservation, A group of 120-150-kDa bands was, after reduction, recogni zed specifically with an antiserum against the matrilin-2-glutathione S-transferase fusion protein in media of the matrilin-2-expressing cel l lines, Assuming glycosylation, this agrees well with the predicted m inimum M(r) of the mature protein (104,300). Immunolocalization of mat rilin-2 in developing skeletal elements showed reactivity in the peric hondrium and the osteoblast layer of trabecular bone. CMP binds both c ollagen fibrils and aggrecan, and because of the similar structure and complementary expression pattern, matrilin-2 is likely to perform sim ilar functions in the extracellular matrix assembly of other tissues.