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 combination of the integrin alpha(L) and beta(2) subunits of LFA-1. Using human/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) subunit and the predicted beta-propeller domain of the alpha(L) subunit. Substitution into mouse LFA-1 of human residues Ser(302) and Arg(303) of the beta(2) subunit and Pro(78), Thr(79), Asp(80), Ile(365), and Asn(367) of the alpha(L) subunit is sufficient to completely reconstitute YTA-1 reactivity. Antibodies that bind to epitopes that are nearby in models of the I-like and beta-propeller domains compete with YTA-1 monoclonal antibody for binding. The predicted beta-propeller domain of integrin alpha subunits contains seven beta-sheets arranged like blades of a propeller around a pseudosymmetry axis. The 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 the I-like domain near the putative Mg(2+) ion binding site. Thus, the I-like domain contacts the bottom or side of the beta-propeller domain near beta-sheets 2 and 3. YTA-1 preferentially reacts with activated LFA-1 and is a function-blocking antibody, suggesting that conformational movements occur near the interface it defines between the LFA-1 alpha and beta subunits.
Zang
Q
Q
Center For Blood Research, Department of Pathology, Harvard Medical School, Boston, Massachusetts 02115, USA.
Lu
C
C
Huang
C
C
Takagi
J
J
Springer
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TA
D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D006801:Humans; D008024:Ligands; D016169:Lymphocyte Function-Associated Antigen-1 / Q000737:chemistry* / Q000378:metabolism; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D016415:Sequence Alignment
D000911:Antibodies, Monoclonal; D008024:Ligands; D016169:Lymphocyte Function-Associated Antigen-1