The use of collagen-based model peptides to investigate platelet-reactive sequences in collagen

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Abstract
Simple collagen‐like peptides comprising a repeat Gly‐Pro‐Hyp sequence are highly platelet‐reactive when presented to platelets in triple‐helical and polymeric form. This activity is not mediated by the platelet collagen receptor integrin α2β1. This may imply the existence of an intrinsic platelet reactivity associated with the collagen triple helix as such or perhaps that the Gly‐Pro‐Hyp sequence in collagen serves as a specific cell‐recognition site. In our view this basic α2β1‐independent reactivity is modulated by the presence in collagen of sequences that may either enhance or diminish the interaction with platelets. Inhibition studies with short linear peptides have allowed the tentative identification of sequences in collagen such as XPGEP(Q)GPX and D(N)GE(Q)X that may promote the activation of platelets and so enhance collagen‐platelet interaction. Sequences serving as integrin α2β1‐binding sites may also promote platelet reactivity by permitting interaction with the collagen receptor. Using triple‐helical peptides based on the sequence of the platelet‐reactive collagen type III fragment α1(III)CB4, we have been able to locate an α2β1‐binding site in collagen type III within a 30‐mer sequence representing residues 508–537 of the α1(III) constituent α‐chain. Despite their α2β1‐independent platelet reactivity, signalling by the (Gly‐Pro‐Hyp)n‐based peptides shows many features in common with signalling by collagen fibers, including activation of p72SYK and p125FAK the latter of which has until now been considered a specific consequence of ligand binding to α2β1. © 1996 John Wiley & Sons, Inc.