Abstract
We have studied binding to collagen of the 59-kDa protein present in most connective tissues. Collagen fibril formation, measured as increasing turbidity, was markedly retarded and reduced by the presence of small amounts of this protein. This was true for both collagen I and collagen II. The effect was also observed when pepsin-treated collagens were used, indicating that interaction with the telopeptides is not involved. The proportion of collagen precipitated in the assay was not or only marginally reduced. Thus, the altered optical properties indicate that structurally different fibrils are formed in the presence of the 59-kDa protein. The 59-kDa protein bound to collagen I or collagen II that had been insolubilized on polystyrene 96-well microtiter plates, as measured by enzyme-linked immunosorbent assay. Analogously, binding to the collagens was demonstrated for the PG-S2 low Mr proteoglycan, previously shown only to inhibit collagen fibrillogenesis. The two matrix components showed similar strength of binding, i.e. Kd 35 nM for the 59-kDa protein and 16 nM for PG-S2 at 20 degrees C. The results do not reveal if the collagen interaction site of the 59-kDa protein is different from that of PG-S2. Our observations do, however, suggest that the 59-kDa protein, as well as PG-S2, have functions related to the regulation of collagen organization in tissues.
Highlights
The results do not reveal if the collagen interaction site of the 59-kDa protein is different from that of PG52
Two different groups have been identified, referred to PG-S1 and PG-S2 (Heinegird et al, 1985).The core proteins of these proteoglycans are of similar size ( M, -45,000), but they are structurally distinct within each group, according to peptide patterns
The small proteoglycans from tendon (DS side chains), sclera (DS side chains), and articular cartilage (DS side chains), representing the PG-S2 species, are all capable of interacting with collagen I and II.*Support forthe physiological relevance of the interaction is the localization of dermatan sulfateproteoglycans at the“d”and “e” bandsof collagen fibrils in nonmineralized connective tissues, e.g. tendon, skin, cornea, and sclera, as revealed by electron microscopy (Scott and Orford, 1981; Scott and Haigh, 1985; Young, 1985)
Summary
CCoollllageCnoC-MbmoaiTnpntinordsienisxnceugCtneiCtCvoMsemooaTlnpltianrosgiensxeuceCntenioC-MvtbmseoaiTnptinordsienisxnceugtneitvCseollageCnoC-MbmoaiTnptinordsienisxnceugtneitvse where K d is the dissociation constant, M is the measured value of absorbance, AA,,, is the maximum absorbance a t saturation, and C is the concentration of free ligand in solution. The molecular mass of PG-S2 used for the calculations was 74,600 Da (Franzbn and Heinegird,1984)
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