Critical amino acid residues for ligand binding are clustered in a predicted beta-turn of the third N-terminal repeat in the integrin alpha 4 and alpha 5 subunits.
Integrin alpha 4 beta 1 is a receptor for vascular cell adhesion molecule (VCAM)-1 and fibronectin (CS-1). The alpha 4 beta 1-ligand interaction is involved in the pathogenesis of diseases and is, therefore, a therapeutic target. Here, we identified critical residues of alpha 4 for ligand binding using alanine-scanning mutagenesis of the previously localized putative ligand binding sites (residues 108-268). Among 43 mutations tested, mutations of Tyr187, Trp188 and Gly190 significantly inhibited cell adhesion to both VCAM-1 and CS-1. This inhibition was not due to any gross structural changes of alpha 4 beta 1. These critical residues are clustered in a predicted beta-turn structure (residues 181-190) of the third N-terminal repeat in alpha 4. The repeat does not contain divalent cation binding motifs. Notably, the mutations within the corresponding region of alpha 5 significantly reduced fibronectin-alpha 5 beta 1 interaction. These findings suggest that the predicted beta-turn structure could be ubiquitously involved in ligand binding of non-I domain integrins.
Irie
A
A
Department of Vascular Biology, Scripps Research Institute, La Jolla, CA 92037, USA.
Kamata
T
T
Puzon-McLaughlin
W
W
Takada
Y
Y
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D016466:CHO Cells; D002448:Cell Adhesion; D006224:Cricetinae; D005353:Fibronectins / Q000378:metabolism*; D006801:Humans; D039041:Integrin alpha4beta1; D016023:Integrins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008024:Ligands; D008969:Molecular Sequence Data; D016296:Mutagenesis; D011487:Protein Conformation; D017469:Receptors, Fibronectin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016201:Receptors, Lymphocyte Homing / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019010:Vascular Cell Adhesion Molecule-1 / Q000378:metabolism*
D000596:Amino Acids; D005353:Fibronectins; D039041:Integrin alpha4beta1; D016023:Integrins; D008024:Ligands; D017469:Receptors, Fibronectin; D016201:Receptors, Lymphocyte Homing; D019010:Vascular Cell Adhesion Molecule-1