Fig. 2. Projection averages of the α₅β₁ headpiece obtained by negative stain EM. The unclasped α₅β₁ headpiece was incubated (A) without or (B) with 1 mM RGD peptide and imaged in the EM. In the +RGD condition, particles with closed (group I) and open (group II) conformations were observed. The three most typical averages for each group are shown, each containing 200–600 particles. Scale bars, 100 Å.