Cartoon models of integrin receptor conformational states and headpiece construct. (A) Three major conformational states of integrin receptor. (B-D) Integrin α_IIbβ₃ headpiece construct, protein purification, and protease digestion. The α_IIbβ₃ headpiece was first purified by Ni-NTA (B), then treated with chymotrypsin and further purified by Ni-NTA and gel filtration (C). It was then treated with carboxypeptidase in the presence of monoclonal antibody 10E5 Fab and finally purified by gel filtration (D). Protein molecular weight markers are in kDa.