Recombinant Human Matrilin-3 Protein, CF

Matrilin-3 is a 50 - 60 kDa extracellular matrix protein that belongs to the superfamily of von Willebrand factor A (VWA) containing proteins. It is primarily expressed in cartilage and functions as a bridging component between proteins of the collagenous matrix (1 - 3). The human Matrilin-3 cDNA encodes a 486 amino acid (aa) precursor with a 28 aa signal sequence, an N-terminal VWA domain, four tandem EGF-like repeats, and a C-terminal coiled coil domain (4). The Matrilins differ in the number of VWA domains (one or two) and EGF-like repeats (one, three, four, or ten) they contain. Human Matrilin-3 shares 82% aa sequence identity with mouse Matrilin-3. Within the first VWA domain, human Matrilin-3 shares approximately 55% aa sequence identity with human Matrilin-1, -2, and -4. The coiled coil domain of Matrilin-3 mediates disulfide-linked homo-oligomerization, with tetramer formation being the most dominant (5 - 7). It can also assemble into hetero-oligomers with Matrilin-1 (5 - 7). Matrilin-3 is more plentiful than Matrilin-1 in the proliferative zone of the growth plate, whereas the reverse is true in the maturation zone (5). Matrilin-3 interacts directly with Collagen IX and COMP (8, 9). In the absence of Collagen IX, the expression of Matrilin-3 is unchanged, although it is retained inside chondrocytes and is not incorporated into the matrix (9). Matrilin-3 also associates with smaller cartilage fibrils independent of Collagen IX (9). Matrilin-3 knockout mice do not display any obvious abnormalities, suggesting that other molecules may compensate for the lack of Matrilin-3 (10). In contrast, intracellular retention of Matrilin-3 with particular point mutations in the VWA domain results in multiple epiphyseal dysplasia (11 - 13). A point mutation in the first EGF-like repeat which has been linked to hand osteoarthritis does not prevent Matrilin-3 secretion (13).