IDENTIFICATION OF A REGULATORY REGION OF INTEGRIN-BETA-1 SUBUNIT USING ACTIVATING AND INHIBITING ANTIBODIES

Members of the beta1 integrin subfamily recognize multiple ligands suc h as fibronectin, laminin, and collagen and mediate cell-cell and cell -extracellular matrix interactions. Beta1 subunit may play a central r ole in regulating beta1 integrin avidity. Here we have identified a sm all region of beta1 subunit (residues 207-218) that is critical for th e binding of both activating (8A2, A1A5, and TS2/16) and inhibiting (4 B4, 4B5, 13, AIIB2, and P4C10) monoclonal antibodies against human bet a1 using interspecies chimeric beta1 and site-directed mutagenesis. Ch icken beta1 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 sit es (residues 120-182 and 220-231), and the amino acid sequence of the region involves a predicted bend structure. The other anti-beta1 antib odies that do not affect cell attachment to ligands (K20, 102DF5, LM44 2, and LM534) recognized the carboxyl-terminal regions of extracellula r domain of beta1 (residues 426-587 for K20 and 588-708 for 102DF5, LM 442, and LM534, respectively). Our data suggest a potential mechanism for the avidity regulation of beta1 integrin through conformational ch anges of beta1 subunit.