Crosslinking of cartilage matrix protein to aggrecan increases with maturation

Abstract

Cartilage matrix protein (CMP) is a trimeric protein occurring in some types of cartilage extracellular matrix (Paulsson and Heinegård 1982). It has recently been purified under native conditions which allowed the proposal of a structural model (Hauser and Paulsson 1994). Early data indicated an interaction of CMP with aggrecan. We now describe the isolation of a complex between CMP and aggrecan from tissue extracts. Proteoglycans prepared from cartilage using conditions minimizing contamination by unrelated proteins consistently contained CMP, apparently associated with the core protein and only partially released upon reduction, even under denaturing conditions. It appears that CMP binds by a nonreducible covalent interaction with one of its subunits to the protein core. Electron microscopy revealed interaction sites for CMP with core protein in the extended domain E2.