The top of the inserted-like domain of the integrin lymphocyte function-associated antigen-1 beta subunit contacts the alpha subunit beta-propeller domain near beta-sheet 3

We find that monoclonal antibody YTA-1 recognizes an epitope formed by a co mbination of the integrin alpha(L) and beta(2) subunits of LFA-1, Using hum an/mouse chimeras of the alpha(L) and beta(2) subunits, we determined that YTA-1 binds to the predicted inserted (I)-like domain of the beta(2) subuni t and the predicted beta-propeller domain of the cu, subunit, Substitution into mouse LFA-1 of human residues Ser(302) and Arg(303) of the beta(2) sub unit and Pro(78), Thr(79) Asp(80), Ile(365), and Asn(367) Of the alpha(L) s ubunit is sufficient to completely reconstitute YTA-1 reactivity. Antibodie s that bind to epitopes that are nearby in models of the I-like and beta-pr opeller domains compete with YTA-1 monoclonal antibody for binding. The pre dicted beta-propeller domain of integrin alpha subunits contains seven beta -sheets arranged like blades of a propeller around a pseudosymmetry axis. T he antigenic residues cluster on the bottom of this domain in the 1-2 loop of blade 2, and on the side of the domain in beta-strand 4 of blade 3. The I domain is inserted between these blades on the top of the beta-propeller domain. The antigenic residues in the beta subunit localize to the top of t he I-like domain near the putative Mg2+ ion binding site. Thus, the I-like domain contacts the bottom or side of the beta-propeller domain near beta-s heets 2 and 3, YTA-1 preferentially reacts with activated LFA-1 and is a fu nction-blocking antibody, suggesting that conformational movements occur ne ar the interface it defines between the LFA-1 alpha and beta subunits.