Abstract
We have previously reported that COMP (cartilage oligomeric matrix protein) is prominent in cartilage but is also present in tendon and binds to collagens I and II with high affinity. Here we show that COMP influences the fibril formation of these collagens. Fibril formation in the presence of pentameric COMP was much faster, and the amount of collagen in fibrillar form was markedly increased. Monomeric COMP, lacking the N-terminal coiled-coil linker domain, decelerated fibrillogenesis. The data show that stimulation of collagen fibrillogenesis depends on the pentameric nature of COMP and not only on collagen binding. COMP interacts primarily with free collagen I and II molecules, bringing several molecules to close proximity, apparently promoting further assembly. These assemblies further join in discrete steps to a narrow distribution of completed fibril diameters of 149 +/- 16 nm with a banding pattern of 67 nm. COMP is not found associated with the mature fibril and dissociates from the collagen molecules or their early assemblies. However, a few COMP molecules are found bound to more loosely associated molecules at the tip/end of the growing fibril. Thus, COMP appears to catalyze the fibril formation by promoting early association of collagen molecules leading to increased rate of fibrillogenesis and more distinct organization of the fibrils.
Highlights
Konung Gustaf V’s 80-årsfond, Anna-Greta Crafoord’s Foundation for Rheumatology Research, Alfred Osterlunds Stiftelse, Greta and Johan Kocks Stiftelser, The Swedish Association against Rheumatology, and the Medical Faculty, Lund University
These chondroitin sulfate chains differ from those found on aggrecan, which are inert with regard to fibrillogenesis and essentially lack the incorporation of chondroitin sulfate E type oversulfated disaccharides [25] as found in perlecan chondroitin sulfate chains
We show that a third type of protein, COMP that is prominent in cartilage [26] as well as in pressure loaded parts of tendon [27, 28], has a novel catalytic stimulatory effect on fibril formation of collagen I and II
Summary
Konung Gustaf V’s 80-årsfond, Anna-Greta Crafoord’s Foundation for Rheumatology Research, Alfred Osterlunds Stiftelse, Greta and Johan Kocks Stiftelser, The Swedish Association against Rheumatology, and the Medical Faculty, Lund University. Ing the native triple helical molecule with retained short telopeptides of only a few amino acids Numerous such collagen molecules assemble laterally in a specific quarter stagger arrangement, initially organizing into microfibrils and subsequently forming fibrils [2], with gap and overlap regions giving a D-periodic banding pattern of 67 nm [3]. Collagen III [14, 15] and the proteoglycans decorin [16, 17], fibromodulin [18, 19], and lumican [20] regulate collagen I fibril formation, reducing fibril thickness. Recent data indicate that fibromodulin may have a catalytic effect on collagen I lateral growth, increasing the fibril thickness [21]. These chondroitin sulfate chains differ from those found on aggrecan, which are inert with regard to fibrillogenesis and essentially lack the incorporation of chondroitin sulfate E type oversulfated disaccharides [25] as found in perlecan chondroitin sulfate chains
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