Function and conformation analyses of an aspartate substitution of the invariant glycine in the integrin βI domain α1-α1′ helix

• Integrin αLβ2-G150D cannot be activated to an extended conformation.
• Integrin αIIbβ3-G161D can be expressed on transfectants.
• Transfectants expressing the αIIbβ3-G161D integrin cannot adhere to fibrinogen.
• The Asp locks the α1-α1′ helices to into a kinked structure.

We showed that the αLβ2 integrin with the non-functional mutation G150D cannot be induced with Mg/EGTA to express the mAb KIM127 epitope, which reports the leg-extended conformation. We extended the study to the αIIbβ3, an integrin without an αI domain. The equivalent mutation, i.e. G161D, also resulted in an expressible, but non-adhesive αIIbβ3 integrin. An NMR study of synthetic peptides spanning the α1-α1′ helix of the β3 I domain shows that both wild-type and mutant peptides are α-helical. However, whereas in the wild-type peptide this helix is continuous, the mutant presents a discontinuity, or kink, precisely at the site of mutation G161D. Our results suggest that the mutation may lock integrin heterodimers in a bent conformation that prevents integrin activation via conformational extension.