Specific Binding of Integrin αvβ3 to the Fibrinogen γ and α_E Chain C-Terminal Domains (original) (raw)

Integrin Rv 3, a widely distributed fibrinogen receptor, recognizes the RGD 572-574 motif in the R chain of human fibrinogen. However, this motif is not conserved in other species, nor is it required for Rv 3-mediated fibrin clot retraction, suggesting that fibrinogen may have other Rv 3 binding sites. Fibrinogen has conserved C-terminal domains in its R (E variant), , and γ chains (designated R E C, C, and γC, respectively), but their function in cell adhesion is not known, except that RIIb 3, a platelet fibrinogen receptor, binds to the γC HHLGGAKQAGDV 400-411 sequence. Here we used mammalian cells expressing recombinant Rv 3 to show that recombinant R E C and γC domains expressed in bacteria specifically bind to Rv 3. Interaction between Rv 3 and γC or R E C is blocked by LM609, a functionblocking anti-Rv 3 mAb, and by RGD peptides. Rv 3 does not require the HHLGGAKQAGDV 400-411 sequence of γC for binding, and R E C does not have such a sequence, indicating that the Rv 3 binding sites are distinct from those of RIIb 3. A small fragment of γC (residues 148-226) supports Rv 3 adhesion, suggesting that an Rv 3 binding site is located within the γ chain 148-226 region. We have reported that the CYDMKTTC sequence of 3 is responsible for the ligand specificity of Rv 3. γC and R E C do not bind to wild-type Rv 1, but do bind to the Rv 1 mutant (Rv 1-3-1), in which the CYDMKTTC sequence of 3 is substituted for the corresponding 1 sequence CTSEQNC. This suggests that γC and R E C contain determinants for fibrinogen's specificity to Rv 3. These results suggest that fibrinogen has potentially significant novel Rv 3 binding sites in γC and R E C.