Binding of collagen alpha1 chains to human platelets.

Abstract

A B S T R A C T We previously reported that purified al chains of type I chick skin collagen induce platelet aggregation. We now describe immunological and biochemical evidence that the peptide binds to intact platelets as an early event in the induction of platelet aggregation and the release reaction.Antibody against al (I) was obtained by immunizing rabbits with complete Freund's adjuvant mixed with purified al. Immunofluorescence studies showed that al(I)-treated platelets exhibited strong immunofluorescence. The intensity of fluorescence was markedly decreased by the pretreatment of platelets with al-CB5 and glucosylgalactosylhydroxylysine.Dose-response curves of platelet aggregation induced by al and the binding of al by washed intact platelets are correlated. The biochemical studies showed that the binding of the al chain to washed intact platelets was platelet concentration and temperature dependent, and that it reached a maximum in 10 min. The process was reversible and specific, with an association constant of 1.7 ,uM. The inhibitor of alinduced platelet aggregation, glucosylgalactosylhydroxylysine, inhibited the al binding. These results suggest that a1(I) chains bind to specific receptor site(s) on platelet membranes to trigger aggregation and the release reaction.

Binding of Chemotactic Collagen-Derived Peptides to Fibroblasts

“…constant of 1.1 x 107/M. The association constant is about 20 times less than that determined for platelets (9).…”

“…As shown in Table I (Fig. 2) which is longer than the time required for a maximal binding of al chain to platelets (9). The binding of al to fibroblasts is also dependent on the concentration of fibroblasts (Fig.…”

“…The dissociated material was chromatographed on agarose A 1.5m (Bio-Rad Laboratories, Richmond, Calif.) and carboxymethyl cellulose columns. The details of these procedures have been reported (9).…”

“…Antisera were raised in rabbits immunized with 1 mgal chains dissolved in 0.5 ml of PBS and emulsified in an equal volume of complete Freund's adjuvant (Difco Laboratories, Detroit, Mich.). The details of this procedure as well as the determination of the antibody titer and specificity have been documented (9).…”

Collagen-mediated platelet aggregation. Evidence for multivalent interactions of intermediate specificity between collagen and platelets.

“…This conclusion is consistent with the recent observation (26) that the platelet-collagen glucosyltransferase requires as substrate the denatured rather than the native form of collagen, since the latter is required to initiate platelet aggregation. The observations of Kang et al (27) and Chiang et al (28,29) on the binding to platelets of chick collagen peptides which contain hydroxysyl glycosides and on their capacity to initiate aggregation are difficult to relate to the well-established requirement for triple-helical structure for platelet aggregation. Furthermore, only chick and not rat (7) or bovine (27) peptides are reportedly effective in initiating aggregation.…”