title: Variation in one residue associated with the metal ion-dependent adhesion site regulates αIIbβ3 integrin ligand binding affinity.
abstract: The Asp of the RGD motif of the ligand coordinates with the β I domain metal ion dependent adhesion site (MIDAS) divalent cation, emphasizing the importance of the MIDAS in ligand binding. There appears to be two distinct groups of integrins that differ in their ligand binding affinity and adhesion ability. These differences may be due to a specific residue associated with the MIDAS, particularly the β3 residue Ala(252) and corresponding Ala in the β1 integrin compared to the analogous Asp residue in the β2 and β7 integrins. Interestingly, mutations in the adjacent to MIDAS (ADMIDAS) of integrins α4β7 and αLβ2 increased the binding and adhesion abilities compared to the wild-type, while the same mutations in the α2β1, α5β1, αVβ3, and αIIbβ3 integrins demonstrated decreased ligand binding and adhesion. We introduced a mutation in the αIIbβ3 to convert this MIDAS associated Ala(252) to Asp. By combination of this mutant with mutations of one or two ADMIDAS residues, we studied the effects of this residue on ligand binding and adhesion. Then, we performed molecular dynamics simulations on the wild-type and mutant αIIbβ3 integrin β I domains, and investigated the dynamics of metal ion binding sites in different integrin-RGD complexes. We found that the tendency of calculated binding free energies was in excellent agreement with the experimental results, suggesting that the variation in this MIDAS associated residue accounts for the differences in ligand binding and adhesion among different integrins, and it accounts for the conflicting results of ADMIDAS mutations within different integrins. This study sheds more light on the role of the MIDAS associated residue pertaining to ligand binding and adhesion and suggests that this residue may play a pivotal role in integrin-mediated cell rolling and firm adhesion.
authors.affiliation: Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana, United States of America ; University of Alabama at Birmingham School of Medicine, Birmingham, Alabama, United States of America.
authors.forename: Joel
authors.initials: J
authors.lastname: Raborn
authors.forename: Ting
authors.initials: T
authors.lastname: Fu
authors.forename: Xue
authors.initials: X
authors.lastname: Wu
authors.forename: Zhilong
authors.initials: Z
authors.lastname: Xiu
authors.forename: Guohui
authors.initials: G
authors.lastname: Li
authors.forename: Bing-Hao
authors.initials: BH
authors.lastname: Luo
mesh_terms: D000409:Alanine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020816:Amino Acid Motifs / Q000235:genetics; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001224:Aspartic Acid / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites / Q000235:genetics; D001667:Binding, Competitive; D002448:Cell Adhesion / Q000235:genetics; D018360:Crystallography, X-Ray; D057809:HEK293 Cells; D006801:Humans; D008024:Ligands; D008670:Metals / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D009154:Mutation; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D013816:Thermodynamics
chemical_list: D008024:Ligands; D008670:Metals; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D001224:Aspartic Acid; D000409:Alanine