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Ligand Binding to Integrins*

The “integrin” terminology was applied in a 1987 review article (1) to describe a family of structurally, immunochemically, and functionally related cell-surface heterodimeric receptors, which integrated the extracellular matrix with the intracellular cytoskeleton to mediate cell migration and adhesion. The three original b subunits (b1, b2, and b3) identified have now expanded to eight, and the number of a subunits stands at 17. These subunits interact noncovalently in a restricted manner to form more than 20 family members. The diversity of integrins is expanded further by alternative splicing, post-translational modifications, and interactions with other cell-surface and intracellular molecules (2–4). The number of integrins and the remarkable breadth of their cellular distribution support the statement that the phenotype of virtually every cell is uniquely influenced by its display of integrins. Over the past 13 years, more than 14,000 scientific articles have dealt with various aspects of integrin biology and almost 1,000 have appeared in the Journal of Biological Chemistry. This article examines a central aspect of integrin biology: ligand recognition and the structural basis for this function.