Abstract
A set of 57 synthetic peptides encompassing the entire triplehelical domain of human collagen III was used to locate binding sites for the collagen-binding integrin alpha(2)beta(1). The capacity of the peptides to support Mg(2+)-dependent binding of several integrin preparations was examined. Wild-type integrins (recombinant alpha(2) I-domain, alpha(2)beta(1) purified from platelet membranes, and recombinant soluble alpha(2)beta(1) expressed as an alpha(2)-Fos/beta(1)-Jun heterodimer) bound well to only three peptides, two containing GXX'GER motifs (GROGER and GMOGER, where O is hydroxyproline) and one containing two adjacent GXX'GEN motifs (GLKGEN and GLOGEN). Two mutant alpha(2) I-domains were tested: the inactive T221A mutant, which recognized no peptides, and the constitutively active E318W mutant, which bound a larger subset of peptides. Adhesion of activated human platelets to GER-containing peptides was greater than that of resting platelets, and HT1080 cells bound well to more of the peptides compared with platelets. Binding of cells and recombinant proteins was abolished by anti-alpha(2) monoclonal antibody 6F1 and by chelation of Mg(2+). We describe two novel high affinity integrin-binding motifs in human collagen III (GROGER and GLOGEN) and a third motif (GLKGEN) that displays intermediate activity. Each motif was verified using shorter synthetic peptides.
Highlights
The collagens in native triple-helical form interact with a subset of the integrins: ␣11, ␣21, ␣101, and ␣111
Several recognition sites have been identified within collagen for ␣11, ␣21, ␣101, and ␣111. They include GXXЈGER motifs, with GFOGER [9] and GLOGER and GASGER [10] being located within the collagen ␣1(I) chain and with GMOGER, GLSGER, and GAOGER being identified from the use of model peptides as integrin-binding sequences [7]
It is important to note that this study does not address potential integrin binding either to the COL2-containing propeptide or to the short non-helical telopeptides of collagen III
Summary
The collagens in native triple-helical form interact with a subset of the integrins: ␣11, ␣21, ␣101, and ␣111. Integrin ␣21, in common with other members of the integrin family, can exist in at least two affinity states that are believed to correspond to the two conformations of the ␣2 I-domain revealed by crystallography [3, 4] In these structures, helix 7 moves axially within the I-domain to adopt two extreme positions, up or down, causing rearrangement of the loops that conceal or expose the MIDAS and so regulate its ligation by GER motifs found in the triple-helical domain of the collagens. Platelet adhesion to collagen III is dependent upon ␣21 under static and shear conditions [15]; the high affinity ␣21-binding sequence GFOGER does not occur in collagen III This raises the question as to how collagen III interacts strongly with the platelet surface. This suggests either direct GPVImediated adhesion to collagen III or GPVI-mediated platelet activation of integrin ␣21, as has been described previously [5]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
