Identification of a regulatory region of integrin β₁ subunit using activating and inhibiting antibodies

Members of the β₁ integrin subfamily recognize multiple ligands such as fibronectin, laminin, and collagen and mediate cell-cell and cell-extracellular matrix interactions, β₁ subunit may play a central role in regulating β₁ integrin avidity. Here we have identified a small region of β₁ subunit (residues 207-218) that is critical for the binding of both activating (8A2, A1A5, and TS2/16) and inhibiting (4B4, 4B5, 13, AIIB2, and P4C10) monoclonal antibodies against human β₁ using interspecies chimeric β₁ and site-directed mutagenesis. Chicken β₁ that has human sequence within residues 207-218 (CH mutant) is recognized by all the human specific antibodies listed above. The region 207-218 is located between the two putative ligand binding sites (residues 120-182 and 220-231), and the amino acid sequence of the region involves a predicted bend structure. The other anti-β₁ antibodies that do not affect cell . attachment to ligands (K20, 102DF5, LM442, and LM534) recognized the carboxyl-terminal regions of extracellular domain of β₁ (residues 426-587 for K20 and 588-708 for 102DF5, LM442, and LM534, respectively). Our data suggest a potential mechanism for the avidity regulation of β₁ integrin through conformational changes of β₁ subunit.