Integrin activation state determines selectivity for novel recognition sites in fibrillar collagens

Abstract

Only three recognition motifs, GFOGER, GLOGER, and GASGER, all present in type I collagen, have been identified to date for collagen-binding integrins, such as α2β1. Sequence alignment was used to investigate the occurrence of related motifs in other human fibrillar collagens, and located a conserved array of novel GER motifs within their triple helical domains. We compared the integrin binding properties of synthetic triple helical peptides containing examples of such sequences (GLSGER, GMOGER, GAOGER, and GQRGER) or the previously identified motifs. Recombinant inserted (I) domains of integrin subunits α1, α2, and α11 bound poorly to all motifs other than GFOGER and GLOGER. Similarly, α2β1-containing resting platelets adhered well only to GFOGER and GLOGER, while ADP-activated platelets, HT1080 cells and two active α2I domain mutants (E318W, locked open) bound all motifs well, indicating that affinity modulation determines the sequence selectivity of integrins. GxO/SGER peptides inhibited platelet adhesion to collagen monomers with order of potency F ≥ L ≥ M > A. These results establish GFOGER as a high affinity sequence, which can interact with the α2I domain in the absence of activation and suggest that integrin reactivity of collagens may be predicted from their GER content.