The cation-binding domain from the alpha subunit of integrin alpha5 beta1 is a minimal domain for fibronectin recognition.
The cation-binding domain from the alpha subunit of human integrin alpha5beta1 was produced as a recombinant protein, alpha5-(229-448). This protein displays a well defined fold with a content of 30-35% alpha-helix and 20-25% beta-strand, based on circular dichroism. The binding of Ca2+ or Mg2+ to alpha5-(229-448) results in a biphasic conformational rearrangement consistent with the occurrence of two classes of cation-binding sites differing by their affinities. The two classes of sites are located in two conformationally independent lobes, as established by a parallel study of two recombinant half-domains (N- and C-terminal) that also adopt stable folds. Upon saturation with divalent cations, alpha5-(229-448) binds an Arg-Gly-Asp (RGD)-containing fibronectin ligand to form a 1:1 complex. Complex formation is associated with a specific conformational adaptation of the ligand, suggesting an induced fit mechanism. In contrast, neither of the half-domains is competent for ligand binding. The alpha5-(229-448)-fibronectin complex is dissociated in the presence of an RGD peptide, as well as of a simple carboxylic acid, suggesting that the RGD aspartyl carboxylate is an essential element that directly interacts with the alpha5 cation-binding domain.
Banères
J L
JL
UPRESA CNRS 5074, Faculté de Pharmacie, 15 Avenue Charles Flahault, 34060 Montpellier Cédex 2, France.
Roquet
F
F
Green
M
M
LeCalvez
H
H
Parello
J
J
D000595:Amino Acid Sequence; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D002413:Cations, Divalent / Q000378:metabolism; D002942:Circular Dichroism; D003001:Cloning, Molecular; D004926:Escherichia coli; D005353:Fibronectins / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D046911:Macromolecular Substances; D008274:Magnesium / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009842:Oligopeptides; D017433:Protein Structure, Secondary; D017469:Receptors, Fibronectin / Q000737:chemistry* / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
D002413:Cations, Divalent; D005353:Fibronectins; D046911:Macromolecular Substances; D009842:Oligopeptides; D017469:Receptors, Fibronectin; D011994:Recombinant Proteins; C047981:arginyl-glycyl-aspartic acid; D008274:Magnesium; D002118:Calcium