Integrin beta(1)-chain residues involved in substrate recognition and specificity of binding to invasin

A highly conserved 14-amino-acid region of the chicken beta(1) integrin cha in (beta(1chk) residues 151-168) hypothesized to be involved in divalent ca tion co-ordination was analysed to determine whether invasin uses the same structural determinants as fibronectin (Fn) to recognize receptors. For the most part, both proteins required similar beta(1) chain residues for integ rin recognition, although the relative preference of the integrin for the t wo substrates could be inverted mutationally. Substitution mutations in the amino terminal residues of this region resulted in defective binding to bo th substrates by the receptor, while substitutions at the carboxyl-terminal end of this region were better tolerated. A derivative carrying the double substitution (KDD160RDV) had the unique phenotype of maintaining Fn bindin g while abolishing invasin binding, indicating that this region of the rece ptor may determine substrate specificity. These data indicate that the inte grin beta(1) chain possesses a ligand binding site shared by invasin and Fn that can be altered by mutation to allow greater preference for the normal ly lower affinity substrate Fn than for invasin. It was also established th at the region analysed has the ability to bind divalent cations.