title: Critical residues of alphaX I-domain recognizing fibrinogen central domain.
abstract: Integrin alphaXbeta2 (CD11c/CD18), which binds several ligands such as fibrinogen and iC3b, has important roles in leukocyte functions including phagocytosis and migration. Establishment of structure and functional relationship in alphaX I-domain, which is a ligand-binding moiety, is important in understanding leukocyte biology and integrin function. Previously we showed that two loops (alpha3-alpha4, betaD-alpha5) around a ligand-binding face of alphaX I-domain are important for the binding of the fibrinogen molecule. In this study, we took the further step of identifying critical residues in these loops and in a supportive loop (betaF-alpha7) for fibrinogen fragment E, the central domain of fibrinogen. The residues S(199) and Q(202) in the alpha3-alpha4 loop and K(243), Y(250) in the betaD-alpha5 loop are critical for the ligand. The residues K(242), D(249), K(251), and D(252) are important but less critical for fibrinogen fragment E. The involvement of the residues in the 3-dimensional model of the I-domain suggests that several amino acid sequences in fibrinogen fragment E are responsible for alphaX I-domain. Sequence comparisons with alphaM I-domain reveal that most of the critical residues shown in alphaX I-domain are also conserved in alphaM and may have important roles in fibrinogen central domain recognition in alphaM I-domain as well.
authors.affiliation: Division of Science Education and Biology, Kangwon National University, Chuncheon, Kangwon-do 200-701, Republic of Korea.
authors.forename: Joo Hee
authors.initials: JH
authors.lastname: Lee
authors.forename: Jeongsuk
authors.initials: J
authors.lastname: Choi
authors.forename: Sang-Uk
authors.initials: SU
authors.lastname: Nham
mesh_terms: D020816:Amino Acid Motifs; D018360:Crystallography, X-Ray; D005340:Fibrinogen / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment
chemical_list: D005340:Fibrinogen