Mutation of a conserved asparagine in the I-like domain promotes constitutively active integrins αLβ2 and αIIbβ3

Abstract

The leukocyte β2 integrins are heterodimeric adhesion receptors required for a functional immune system. Many leukocyte adhesion deficiency-1 (LAD-1) mutations disrupt the expression and function of β2 integrins. Herein, we further characterized the LAD-1 mutation N329S in the β2 inserted (I)-like domain. This mutation converted αLβ2 from a resting into a high affinity conformer because αLβ2N329S transfectants adhered avidly to ligand intercellular adhesion molecule (ICAM)-3 in the absence of additional activating agent. An extended open conformation is adopted by αLβ2N329S because of its reactivity with the β2 activation reporter monoclonal antibodies MEM148 and KIM127. A corresponding mutationin β3 generated constitutively active αIIbβ3 that adhered to fibrinogen. This Asn is conserved in all human β subunits, and it resides before the last helix of the I-like domain, which is known to be important in activation signal propagation. By mutagenesis studies and review of existing integrin structures, we conjectured that this conserved Asn may have a primary role in shaping the I-like domain by stabilizing the conformation of the α7 helix and the β6-α7 loop in the I-like domain. © 2007 by The American Society for Biochemistry and Molecular Biology, Inc.