The very late antigen family of heterodimers is part of a superfamily of molecules involved in adhesion and embryogenesis

The very late antigen (VLA) protein family contains at least five related heterodimers, including a fibronectin receptor structure, and probably other cell substrate adhesion receptors. These cell-surface VLA proteins were immunopurified from human placenta (VLA-1, VLA-3, and VLA-5), platelets (VLA-2), and Molt-4 cells (VLA-4) using a series of monoclonal antibody-Sepharose immunoaffinity columns. After further purification by gel electrophoresis, the N-terminal amino acid sequence for each of the five VLA α subunits was determined. In the first 14 positions, the five VLA α subunits showed an average of 42% homology to each other, rising to 59% including conservative amino acid substitutions. In addition, the α subunits from (i) the LFA-1, Mac-1 (CR-3), and p150,95 family of heterodimers, (ii) the vitronectin receptor-platelet GPIIb/IIIa family, and (iii) a position-specific (PS) antigen important in Drosophila embryogenesis each showed average homologies of 31-40% to individual VLA α sequences and 46-52% homology to VLA α subunits including conservative substitutions. Taken together, these results suggest that (i) the VLA proteins, (ii) the LFA-1, Mac-1, and p150,95 family, (iii) the GPIIb/IIIa, vitronectin receptor family, and (iv) the Drosophila PS antigens have evolved as four subgroups in a highly conserved supergene family of receptors involved in fundamentally important functions, such as cell adhesion, migration, and embryogenesis.