Identification of a regulatory region of integrin beta 1 subunit using activating and inhibiting antibodies.

Members of the beta 1 integrin subfamily recognize multiple ligands such as fibronectin, laminin, and collagen and mediate cell-cell and cell-extracellular matrix interactions. beta 1 subunit may play a central role in regulating beta 1 integrin avidity. Here we have identified a small region of beta 1 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 beta 1 using interspecies chimeric beta 1 and site-directed mutagenesis. Chicken beta 1 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-beta 1 antibodies that do not affect cell attachment to ligands (K20, 102DF5, LM442, and LM534) recognized the carboxyl-terminal regions of extracellular domain of beta 1 (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 beta 1 integrin through conformational changes of beta 1 subunit.