DIFFERENTIAL-EFFECTS OF INTEGRIN ALPHA-CHAIN MUTATIONS ON INVASIN ANDNATURAL LIGAND INTERACTION

To determine if recognition of the Yersinia pseudotuberculosis invasin protein and natural substrates requires identical integrin residues, a region of the human alpha(3) integrin chain predicted to be involved in substrate adhesion was targeted for mutation. One point mutation l ocated in a region of the third N-terminal repeat of the alpha(3) chai n, alpha(3)-W220A, failed to promote adhesion to the natural alpha(3)b eta(1) substrate epiligrin but maintained near wild type levels of adh esion to invasin, A second nearby mutation, alpha(3)-Y218A, which show ed no detectable adhesion to epiligrin, was only partially attenuated for invasin binding as well as invasin-mediated bacterial uptake. A th ird substitution, alpha(3)-D154A, predicted to be in the second N-term inal repeat not known to be implicated in cell adhesion, was competent for invasin-promoted adhesion events and appeared to encode a recepto r of increased activity, as it had a higher efficiency than wild type receptor for adhesion to epiligrin, Cell lines expressing this derivat ive were not recognized by a function blocking anti-alpha(3) antibody, indicating that the second and third repeats of the alpha(3) chain ar e either closely linked in space or the second repeat can modulate act ivity of the third. Differential effects on substrate adhesion do not appear to be associated with all integrin alpha chain mutations, as al pha(4) chain mutations affecting the divalent cation binding domains d epressed adhesion to invasin to a significant extent.