Identification of the Binding Site for Fibrinogen Recognition Peptide γ383–395 within the αMI-Domain of Integrin αMβ2

The leukocyte integrin αMβ2 (Mac-1, CD11b/CD18) is a cell surface adhesion receptor for fibrinogen. The interaction between fibrinogen and αMβ2 mediates a range of adhesive reactions during the immune-inflammatory response. The sequence γ383TMKIIPFNRLTIG395, P2-C, within the γ-module of the D-domain of fibrinogen, is a recognition site for αMβ2 and αXβ2. We have now identified the complementary sequences within the αMI-domain of the receptor responsible for recognition of P2-C. The strategy to localize the binding site for P2-C was based on distinct P2-C binding properties of the three structurally similar I-domains of αMβ2, αXβ2, and αLβ2,i.e. the αMI- and αXI-domains bind P2-C, and the αLI-domain did not bind this ligand. The Lys245-Arg261 sequence, which forms a loop βD-α5 and an adjacent helix α5 in the three-dimensional structure of the αMI-domain, was identified as the binding site for P2-C. This conclusion is supported by the following data: 1) mutant cell lines in which the αMI-domain segments 245KFG and Glu253-Arg261 were switched to the homologous αLI-domain segments failed to support adhesion to P2-C; 2) synthetic peptides duplicating the Lys245-Tyr252 and Glu253-Arg261 sequences directly bound the D fragment and P2-C derivative, γ384–402, and this interaction was blocked efficiently by the P2-C peptide; 3) mutation of three amino acid residues within the Lys245-Arg261 segment, Phe246, Asp254, and Pro257, resulted in the loss of the binding function of the recombinant αMI-domains; and 4) grafting the αM(Lys245-Arg261) segment into the αLI-domain converted it to a P2-C-binding protein. These results demonstrate that the αM(Lys245-Arg261) segment, a site of the major sequence and structure difference among αMI-, αXI-, and αLI-domains, is responsible for recognition of a small segment of fibrinogen, γThr383-Gly395, by serving as ligand binding site. The leukocyte integrin αMβ2 (Mac-1, CD11b/CD18) is a cell surface adhesion receptor for fibrinogen. The interaction between fibrinogen and αMβ2 mediates a range of adhesive reactions during the immune-inflammatory response. The sequence γ383TMKIIPFNRLTIG395, P2-C, within the γ-module of the D-domain of fibrinogen, is a recognition site for αMβ2 and αXβ2. We have now identified the complementary sequences within the αMI-domain of the receptor responsible for recognition of P2-C. The strategy to localize the binding site for P2-C was based on distinct P2-C binding properties of the three structurally similar I-domains of αMβ2, αXβ2, and αLβ2,i.e. the αMI- and αXI-domains bind P2-C, and the αLI-domain did not bind this ligand. The Lys245-Arg261 sequence, which forms a loop βD-α5 and an adjacent helix α5 in the three-dimensional structure of the αMI-domain, was identified as the binding site for P2-C. This conclusion is supported by the following data: 1) mutant cell lines in which the αMI-domain segments 245KFG and Glu253-Arg261 were switched to the homologous αLI-domain segments failed to support adhesion to P2-C; 2) synthetic peptides duplicating the Lys245-Tyr252 and Glu253-Arg261 sequences directly bound the D fragment and P2-C derivative, γ384–402, and this interaction was blocked efficiently by the P2-C peptide; 3) mutation of three amino acid residues within the Lys245-Arg261 segment, Phe246, Asp254, and Pro257, resulted in the loss of the binding function of the recombinant αMI-domains; and 4) grafting the αM(Lys245-Arg261) segment into the αLI-domain converted it to a P2-C-binding protein. These results demonstrate that the αM(Lys245-Arg261) segment, a site of the major sequence and structure difference among αMI-, αXI-, and αLI-domains, is responsible for recognition of a small segment of fibrinogen, γThr383-Gly395, by serving as ligand binding site. Integrin αMβ2 participates in the attachment of leukocytes to the endothelial lining of blood vessels and the subsequent transmigration of adherent cells during immune-inflammatory responses (1Anderson D.C. Schmalsteig F.C. Shearer W. Becker-Freeman K. Kohl S. Smith C.W. Tosi M.F. Springer T. Fed. Proc... 1985; 44: 2671-2677Google Scholar, 2Anderson D.C. Springer T.A. Annu. Rev. Med... 1987; 38: 175-194Google Scholar, 3Hogg N. Stewart M.P. Scarth S.L. Newton R. Shaw J.M. Law S.K.A. Klein N. J. Clin. Invest... 1999; 103: 97-106Google Scholar). The engagement of fibrinogen (Fg)1 by αMβ2 on the surface of leukocytes and by intercellular adhesion molecule-1 (ICAM-1) on the endothelium may play a role in mediating the adhesion of leukocytes to the vessel wall (4Languino L.R. Plescia J. Duperray A. Brian A.A. Plow E.F. Geltosky J.E. Altieri D.C. Cell.. 1993; 73: 1423-1434Google Scholar,5Sriramarao P. Languino L.R. Altieri D.C. Blood.. 1996; 88: 3416-3423Google Scholar) and in facilitating their subsequent extravasation across the endothelial monolayer (6Languino L.R. Duperray A. Joganic K.J. Fornaro M. Thornton G.B. Altieri D.C. Proc. Natl. Acad. Sci. U. S. A... 1995; 92: 1505-1509Google Scholar). In addition, the binding of deposited fibrinogen or fibrin to αMβ2 may mediate leukocyte adhesion at extravascular sites of inflammation (7Bini A. Fenoglio Jr., J.J. Mesa-Tejada R. Kudryk B. Kaplan K.L. Arteriosclerosis.. 1989; 9: 109-121Google Scholar, 8Valenzuela R. Shainoff J.R. DiBello P.M. Urbanic D.A. Anderson J.M. Matsueda G.R. Kudryk B.J. Am. J. Pathol... 1992; 141: 861-880Google Scholar, 9Wu X. Helfrich M.H. Horton M.A. Feigen L.P. Lefkowith J.B. J. Clin. Invest... 1994; 94: 928-936Google Scholar). In previous studies, Altieri et al. (10Altieri D.C. Agbanyo F.R. Plescia J. Ginsberg M.H. Edgington T.S. Plow E.F. J. Biol. Chem... 1990; 265: 12119-12122Google Scholar, 11Altieri D.C. Plescia J. Plow E.F. J. Biol. Chem... 1993; 268: 1847-1853Google Scholar) demonstrated that a peptide (designated P1), corresponding to residues 190–202 of the γ-chain of the D-domain of Fg, was recognized by αMβ2. However, when residues key to the recognition of P1 by αMβ2-bearing cells were mutated in the γ-module, γ148–411, this recombinant fragment was as active as its wild-type counterpart in supporting αMβ2-mediated adhesion (12Ugarova T.P. Solovjov D.A. Zhang Plow E.F. J. Biol. Chem... Scholar). This to the for αMβ2 recognition sites within the and the corresponding to was identified (12Ugarova T.P. Solovjov D.A. Zhang Plow E.F. J. Biol. Chem... Scholar). in was P1 in adhesion of the cells to the D fragment of of the of peptides that its γ383TMKIIPFNRLTIG395, P2-C, was the site of its (12Ugarova T.P. Solovjov D.A. Zhang Plow E.F. J. Biol. Chem... Scholar). a leukocyte αXβ2, which is homologous to αMβ2, was demonstrated to bind to the γ-module and P2-C peptide P. P. N. Acad. Sci. and P2-C peptide efficiently blocked the the αMβ2 the a of amino acid in the to the recognition of by αMβ2 J. Springer T.A. J. 1993; Scholar) and to the binding of to this integrin J. Springer T.A. J. 1993; Scholar, Plescia J. Altieri D.C. J. Biol. Chem... 1994; Scholar). In to Fg, this was in the binding of T. P. J. M.A. Proc. Natl. Acad. Sci. U. S. A... 1994; and P. T. M.A. J. 1994; Scholar, Zhang Plow E.F. M. J. Biol. Chem... 1994; Scholar). We have that the recombinant αMI-domain and that blocked this interaction (12Ugarova T.P. Solovjov D.A. Zhang Plow E.F. J. Biol. Chem... Scholar). that not sites in the recognition of and Plow E.F. J. Biol. Chem... 1996; Scholar). However, the binding sites for and in the αMI-domain were P. T. M.A. J. Biol. Chem... 1996; Scholar, S.L. J. Biol. Chem... 1995; Scholar, Plow E.F. J. Biol. Chem... Scholar, R. P. M.A. J. the recognition site for not sequences key to the binding of and to the αMI-domain were a strategy Plow E.F. J. Biol. Chem... Scholar, Plow E.F. 1999; 38: Scholar). This is based the of the I-domains of and and the in their ligand the of the I-domains of and similar P. M.A. R. Cell.. 1995; Scholar, M.A. 1995; Scholar, A. Proc. Natl. Acad. Sci. U. S. A... 1995; 92: Scholar, A. 1996; the of P. T. M.A. J. 1994; Zhang Plow E.F. M. J. Biol. Chem... 1994; Scholar). Fg, and not bind to that in the structure of the αMI- and may responsible for their in ligand binding In this have to localize the binding site for the P2-C sequence of within the The strategy was based on the in the binding of P2-C to the αMI-, αXI-, and and of mutant synthetic and the The binding site for P2-C was within the segment a site of the major structure between αMI-, αXI-, and The grafting of this segment into the αLI-domain converted it to the P2-C-binding protein. a small amino acid sequence, P2-C, a structure within a of fibrinogen D.C. Scholar) is to a small segment that a structure within the cells wild-type and the mutant forms of the αMβ2 receptor were and in Plow E.F. J. Biol. Chem... 1996; Scholar, Plow E.F. J. Biol. Chem... Scholar). These cells were as adherent in and was blood by Scholar) or The fragment was by of and as T.P. J. Biol. Chem... 1992; Scholar). The fragment was by of the This fragment amino acid residues the of the γ-chain and P. P. B. and in to the P1 P2-C and peptides were and as (12Ugarova T.P. Solovjov D.A. Zhang Plow E.F. J. Biol. Chem... Scholar). In addition, an of P2-C, a peptide the γ384–402, was to for binding to αMI-domain The following peptides duplicating sequences within the αMI-domain were The the of the residues within the to et al. M.A. J. was to the and were R. Kudryk B. S. B. Blood.. Scholar) was a B. the and G.R. P. and Scholar) was Matsueda The I-domains were as and of by The for the αMI-domain and αLI-domain were by reactions as Plow E.F. J. Biol. Chem... 1996; Scholar) and which the for the of and The for the αMI-domain were and The for the αLI-domain were and The and recognition sequences that were in the The were and and in the The of the sequence was by The was in and was by for at the the following were to a fragment the a of cell and The was and and into The was in and the of the was by The was and the cell as a the for the αMI- and of the αMI-domain was by The the αMI-domain was by the The in the αMI-domain and the in The complementary to of the were during by the was to the The the was into the and was by The cells were the mutant and the mutant were as for the recombinant wild-type The of wild-type and mutant recombinant I-domains was by and T.P. Ginsberg M.H. Plow E.F. J. Biol. Chem... 1993; 268: in the Lys245-Arg261 sequence of the recombinant αMI-domain and sequences for their the of amino in the the The the of amino in the M.A. J. The the in a The segment corresponding to the sequence within the was to the homologous segment of the αMI-domain The segment was by The of the was based on the that sequence corresponding to αM(Lys245-Arg261) a site for the site for this is between and of the the Lys245-Arg261 to the were to site within the αM(Lys245-Arg261) segment and sequences in and the site for is The the αLI-domain was by the following for for for the was to the The was and to the These were and into The of the sequence and the of the were by The cells were the mutated and the was following the for the wild-type and mutant were to the of αMβ2 on the surface of the cells wild-type and mutant forms of the The cells were and cells were or at of cell for at The cells were and a for at the cells were and in a of cells a similar of the receptor were by of mutant was by in the of the αMβ2 was by The of were and P2-C peptide or and of fragment for at The of peptides the was by peptides (12Ugarova T.P. Solovjov D.A. Zhang Plow E.F. J. Biol. Chem... Scholar). The were for at The cells wild-type or mutated forms of αMβ2 were for at and in and at in and and of the cells were to and on the adhesive for at in a The cells were by three The adherent cells were at and by the of a the The was in a and the of adherent cells was a to the were cells (12Ugarova T.P. Solovjov D.A. Zhang Plow E.F. J. Biol. Chem... and the results were to the the interaction of the wild-type mutant and were P2-C or at at and or for The in and were to the and for at bound I-domains were an at a to was for and the binding of the I-domains was by a the binding of to P2-C was that of wild-type αMI-domain, and binding to or was the interaction of the D fragment the were peptides and Glu253-Arg261 at at and for at in and were to the and for at In the of the was of or and to the αMI-domain to was and for at binding was by the at demonstrate the binding of the P2-C to the αMI-domain were as of the γ384–402, in and were to αMI-domain peptides and for at the binding of the was The an within this it P2-C. P. and T. P. The binding of this to was by to and for of adherent cells bound to as and based on to αMβ2 cell at In previous studies, have demonstrated that the P2-C peptide directly to the recombinant αMI-domain (12Ugarova T.P. Solovjov D.A. Zhang Plow E.F. J. Biol. Chem... Scholar). P2-C P. P. N. Acad. Sci. the role of the in this interaction was not and the recognition of P2-C by the αLI-domain not the three I-domains were as and for their to the P2-C in the recombinant a and binding to the P2-C peptide similar to that of the recombinant In the recombinant αLI-domain did not P2-C at the of the αLI-domain The binding of the I-domains the binding properties of the corresponding on cell the and cells to and P2-C, the cells not and that binding of P2-C to homologous αMβ2 and αXβ2, is by αMI- and and that the of binding of P2-C to may the of sequence of the mutant and the cells wild-type adhesive of cells wild-type αMβ2 and in and were in the of of P2-C. of cells to is for at in a the cells were by three and the of adherent cells was the as as a of cells and the of The of P2-C and the were as (12Ugarova T.P. Solovjov D.A. Zhang Plow E.F. J. Biol. Chem... Scholar) and on the of the wild-type and the αMI-domain to P2-C and of cells were to the and of peptide and and was as in of mutant the at of P2-C and at of the The results as a of adhesion the wild-type cells at of the P2-C and lines on at the of adhesion the wild-type and lines the of adhesion cells of the cells and is for mutant to adhesion in at the to the binding site for P2-C within the αMI-domain, mutant cell a mutant αMβ2 in which a αMI-domain sequence was for the corresponding of the were for their adhesion to P2-C or These mutant cell lines have to the binding of and to αMβ2 Plow E.F. J. Biol. Chem... Scholar, Plow E.F. 1999; 38: Scholar). to cell lines and similar of wild-type and mutant were by cell and by by The of the as by the in by the wild-type The adhesion of mutant was of P2-C and fragment to the of In a cell a mutant receptor did to the adhesion was the of the ligand and a This adhesion was that of the cells wild-type αMβ2 receptor and cells in the to of The cell lines adhesion similar to or the wild-type αMβ2 cells were identified as The of cell adhesion to P2-C for wild-type αMβ2 and a is in of to P2-C was and of cells adherent to P2-C at the of wild-type and mutant cells to a was and was to of as the the cells to adhesive P2-C and of of interaction of did not to P2-C; adhesion of cells was similar to that of The results of adhesion of to P2-C and the fragment in and B. The as the adhesion of the wild-type cells to for the following of αMI-domain and These cell lines a of The of adhesion of was not the of surface of the receptor was between adhesion and surface of was that of the wild-type αMβ2 adhesion was the surface of the was that of the cells the wild-type adhesion was of and was similar to that of the wild-type The following supported the or of adhesion to P2-C the cells the wild-type αMβ2 receptor mutant and of and was the of adhesion to P2-C and of wild-type αMβ2 These were as was the mutant to recognition of P2-C and the D it supported adhesion to P2-C adhesion to In subsequent on the corresponding to the wild-type αMI-domain sequences were and for their to the D fragment and P2-C. the sequences within of the and were peptide was the the sequence of the mutant was at its to the peptides were and In a of the which a for the P2-C in the of the which at in the in These αMI-domain peptides were and the binding of fragment to was in Lys245-Tyr252 and bound The binding of and and peptide did not bind the The interaction of the fragment Lys245-Tyr252 and Glu253-Arg261 was The binding of to Lys245-Tyr252 and Glu253-Arg261 was by P2-C and which the P2-C sequence of binding to Glu253-Arg261 by is In addition, P1 the binding of to Lys245-Tyr252 and Glu253-Arg261 the of P1 on the binding to Glu253-Arg261 is peptides duplicating fibrinogen sequences and did not the P1 the interaction as efficiently as of this peptide to for binding to αMβ2 (12Ugarova T.P. Solovjov D.A. Zhang Plow E.F. J. Biol. Chem... Scholar). The interaction of the αMI-domain peptides was in the of binding was in the in the of or did not binding of the fragment to the Lys245-Tyr252 and Glu253-Arg261 peptides at as as it efficiently adhesion of the cells to the D fragment and P2-C peptide at a as as These that not the which of binding P2-C and the when binding of to the αMI-domain peptides was did not bind to Lys245-Tyr252 and Glu253-Arg261 peptides of and on the binding of fragment and the P2-C derivative, γ384–402, to fragment in or in was to the for at bound was to and The of on the binding of the fragment in the of was in The of P2-C and P1 is for The binding of the was by the as in The the of the at of a in in a fragment in or in was to the for at bound was to and The of on the binding of the fragment in the of was in The of P2-C and P1 is for The binding of the was by the as in The the of the at of a in In addition, were to binding of P2-C to the αMI-domain a peptide γ384–402, which an for the demonstrated that efficiently bound to Lys245-Tyr252 and Glu253-Arg261 in a and The binding of to was and peptide did not bind to the interaction of the the binding of to Lys245-Tyr252 and Glu253-Arg261 was the that the binding of to Lys245-Tyr252 and Glu253-Arg261 was fibrinogen and These peptides sequences that in to and integrin These peptides an at recognized by the G.R. P. and Scholar). and did not bind to the αMI-domain peptides as by the of the for the of the interaction between and αMI-domain Lys245-Tyr252 and the and bound to the peptides within the αMI-domain, Lys245-Tyr252 and and the interaction of peptides the This is the binding of the fragment by P2-C. We have to that the identified αMI-domain Lys245-Tyr252 and a binding site for P2-C. by the structure of the αMI- and αLI-domains, the Lys245-Arg261 segment was switched the αMI-domain into the counterpart of the The sequence of the mutated was and the was as a protein. The of this is in A. The P2-C peptide was and the binding of the and the αLI-domain was the αLI-domain not bind to P2-C, the grafting of the segment the P2-C binding function to the the of the interaction not the the of the P2-C to of the binding was similar to that for wild-type αMI-domain, for the for the wild-type The interaction of the P2-C was blocked by P2-C, The residues within the αM(Lys245-Arg261) segment, responsible for the P2-C were identified by The of residues for was based on the following 1) the of residues that in of P2-C on the surface of the 2) the in the binding function between and it is that the residues that P2-C or between 3) the of segment did not adhesion of mutant cell this sequence was not in Phe246, Asp254, Pro257, and on the surface of the αMI-domain in the and residues in the αM(Lys245-Arg261) and sequences of the residues in Lys245-Arg261 segment and between and Asp254, Pro257, and the of residues in the ligand binding or to were into the αMI-domain and the of mutant to the P2-C was The binding of or of and and was wild-type In I-domains of and bound to the wild-type the of 245KFG adhesion of the cells and in P2-C was mutated to previous that of to the binding of the αMI-domain to mutation to was R. P. M.A. J. Scholar). in the binding of the αMI-domain mutation was The binding of the three and to P2-C was not by in based the following 1) The of the mutant I-domains and was similar to that the wild-type αMI-domain was for in this P. T. M.A. J. Biol. Chem... 1996; Scholar). 2) of the three-dimensional structure of the αMI-domain that of not of the three mutated residues not residues and not into the of the α5 3) major within a loop and Annu. Rev. 1999; Scholar). that the three Phe246, Asp254, and Pro257, directly in the P2-C In this have identified key of the binding site for a small amino acid sequence of Fg, within the αMI-domain of αMβ2. The strategy to the ligand binding site was based on the difference in the P2-C binding properties of the αMI-, αXI-, and and complementary In the a of to the binding for and Plow E.F. J. Biol. Chem... Scholar, Plow E.F. 1999; 38: Scholar, Plow E.F. Zhang J. were for adhesion to P2-C and fragment of In segments the αMI-domain were the corresponding segments the homologous which not bind of segments at the surface of the αMI-domain, sequences for interaction the ligand. the to support adhesion to P2-C and and αMI-domain segments may for binding of of three and resulted in the loss of adhesive These segments may play an role in ligand the by mutant that the P2-C binding within the αMI-domain was of on the structure of the αMI-domain P. M.A. R. Cell.. 1995; the segments for recognition a of helix the loop between helix and helix the segment in the loop between helix and and the helix These sequences an on the of the αMI-domain in of in The the of synthetic peptides duplicating the sequences of the segments in the These that of and may amino acid residues that directly in binding the P2-C sequence of the peptides that Lys245-Tyr252 and bound P2-C. the peptide did not the and the results not a role for peptides in binding the peptide may not the for recognition by the ligand. The Lys245-Tyr252 and Glu253-Arg261 sequences and the αM(Lys245-Arg261) sequence as the binding site for P2-C. this segment is the between the αMI- and in of sequence and In of helix which is by residues of A. Proc. Natl. Acad. Sci. U. S. A... 1995; 92: Scholar, A. 1996; Scholar). In addition, the loop βD-α5 is in in and a this difference between and for of to bind that the βD-α5 helix in the αMI-domain the binding site for the the grafting of the Lys245-Arg261 segment into the corresponding of the demonstrated in this P2-C binding to the and the binding of the receptor for P2-C was similar to that of wild-type the role of the βD-α5 helix in P2-C which was the was by the the of the the it the that the is for P2-C binding of the three residues resulted in the loss of P2-C it Phe246, Asp254, and as the the role of the βD-α5 helix in the P2-C binding and that three residues in ligand is of the and resulted in the loss of function that and support The of the of and on P2-C recognition of of the ligand binding in the In this a of the structure of and was by an the In to the P. M.A. R. Cell.. 1995; which is to for the binding function S.L. J. Biol. Chem... 1995; Scholar, M. M.A. Cell.. 1993; in the may ligand binding by S.L. J. Biol. Chem... 1995; Scholar, M. M.A. Cell.. 1993; Scholar, M. T. J. Biol. Chem... 1995; Scholar). of or the residues that not on the surface of the αMI-domain, the binding of to S.L. J. Biol. Chem... 1995; that a have in the small in the of the to in binding αM(Lys245-Arg261) in to the binding of the residues in this sequence is directly in of the P. M.A. R. Cell.. 1995; Scholar). results that the binding of the D fragment and P2-C, to peptides duplicating Lys245-Arg261 was This is previous that or mutation of a which to the bound the binding of to the αMI-domain it the binding of and to the recombinant fragment P. M.A. R. Cell.. 1995; Scholar). that bind to I-domains of duplicating βD-α5 loop in the αMI-domain or it bound to in a T. P. J. M.A. Proc. Natl. Acad. Sci. U. S. A... 1994; Scholar). at in the of P2-C, its binding to the αMI-domain not interaction the as was P. M.A. R. Cell.. 1995; Scholar). This conclusion is supported by the that P2-C sequence in not a to a to the the P2-C an which a the structure of the M. M. 1999; Scholar). The sequence which the identified was in the binding of of of αMβ2 S.L. J. Biol. Chem... 1995; Scholar). In addition, mutation of to Plow E.F. 1999; 38: Scholar) and to Plow E.F. 1999; 38: Scholar) However, the binding site for the binding the of this in recognition of to did not adhesion to P2-C or fragment in it to binding Plow E.F. J. Biol. Chem... 1996; Scholar). The of the and binding sites within the αMI-domain was based on the of to interaction of the αMβ2-bearing cells Zhang Plow E.F. M. J. Biol. Chem... 1994; Scholar, Plow E.F. J. Biol. Chem... 1996; Scholar). The segments which were identified as for and have to in binding Plow E.F. J. Biol. Chem... Scholar). The in the binding of αMI-domain to 1) of which adhesion to was not for and 2) of which was not for adhesion to The binding site for was by grafting the identified segments into the binding to the receptor Plow E.F. J. Biol. Chem... Scholar). However, the identified segments were it is of sequences sites or may to a for did not the binding of the D fragment or P2-C to Lys245-Tyr252 and Glu253-Arg261 that segments of the αMI-domain may not sites for is that the binding site for may in the identified and and for and Plow E.F. J. Biol. Chem... Scholar). the of the mutant or mutant was and Plow E.F. J. Biol. Chem... Scholar). In addition, al. P. T. M.A. J. Biol. Chem... 1996; Scholar) demonstrated the of and which or within and for The of this is that and P2-C not for the binding site on the αMI-domain that adhesion to by or the for the was to a that within and and within the segment Springer T.A. Proc. Natl. Acad. Sci. U. S. A... 1999; Scholar). This the αMβ2-mediated adhesion to Springer T.A. J. 1993; Scholar). the for the which the active and binding of to leukocytes in the sequence J. Altieri D.C. J. Biol. Chem... Scholar). this in the αMI-domain may a that ligand recognition to of the In have the binding site for the P2-C sequence of Fg, within the αMI-domain of αMβ2. The binding site was in the sequence, the site to a on the of the The interaction between P2-C and the αMI-domain Lys245-Arg261 may a recognition complementary binding sites within the αMI-domain and ligand. The αM(Lys245-Arg261) sequence is a of the major difference between the I-domains of αMβ2 and in of sequence and the of may the ligand We for the mutant cells B. Kudryk for Matsueda for and for We for were at the a the W. M. fibrinogen intercellular adhesion molecule-1 of residues in the of αMβ2, αXβ2, and cell