Cartilage Matrix Assembly: Evidence for Binding of Matrilin-3 to Collagens Ix and Xi

Introduction Matrilin-3 is a member of the newly defined matrilin family of extracellular matrix proteins. All matrilin family members consist of one or two von Willebrand factor type A-like domain(s), 1-10 epidermal growth factor-like domain(s) and a C-terminal coiled-coil oligomerization domain (1). Matrilin-1 (also known as CMP) and matrilin-3 are prominent matrix components of growth cartilages. Several different molecular forms of matrilin have been identified in growth cartilage, including the homotrimer of matrilin-1, homotetramer of matrilin-3, and heterotetramers of matrilin-1 and 3 (2-4). Matrilin-1 trimer is known to bind to type II collagen fibrils and to aggrecan in the extracellular matrix of cartilage and also to form a filamentous polymer by itself (5,6). The function of matrilin-3 is unknown but the fact that it differs from matrilin-1 in number of vWFA-like and EGF-like domains and in molecular assembly suggests that matrilin-3 tetramers differ from matrilin-1 trimers in their interactive properties in the matrix. Matrilin-3 is reported to bind to collagens II and IX but with higher affinity to collagen IX (7). Here we explore further the ability of matrilin-3 to bind to different cartilage collagen types.