Asp-698 and Asp-811 of the integrin alpha4-subunit are critical for the formation of a functional heterodimer.
The amino acid motif LDV is the principal binding site for alpha4 integrins in fibronectin, and homologous motifs are recognized in vascular cell adhesion molecule-1 and MAdCAM-1. Three conserved LDV motifs (LDV-1 to 3) occur in the ectodomain of the human and mouse alpha4-subunit, the functions of which are unknown. We demonstrate here that alpha4-transfected fibroblasts with mutation in LDV-1 (D489N) behaved like alpha4-wild type but that LDV-2 (D698N) and LDV-3 (D811N) mutants were impaired in binding and spreading on alpha4-specific substrates. On the RGD-containing fibronectin fragment FN-120 there was an inverse behavior; now the alpha4-wild type and the LDV-1 mutant could not adhere whereas the two other mutants could. The beta1 chain was critical for the differential integrin response. Biochemical analysis demonstrated that the LDV-2 and -3 mutations reduced the strength of the alpha4beta1 association, favored the formation of alpha5beta1, and prevented the expression of alpha4beta7 on the cell surface. Our results indicate that LDV-2 and LDV-3 are critical for the formation of a functional heterodimer. The presence of similar amino acid motifs in ligands and the alpha4-subunit suggest that metal coordination plays an important role in integrin-ligand binding as well as for heterodimer formation.
Zeller
Y
Y
Tumor Immunology Programme, 0710, German Cancer Research Center, D-69120 Heidelberg, Federal Republic of Germany.
Lohr
J
J
Sammar
M
M
Butcher
E C
EC
Altevogt
P
P
D016475:3T3 Cells; D000818:Animals; D015703:Antigens, CD / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001224:Aspartic Acid / Q000737:chemistry / Q000378:metabolism*; D002448:Cell Adhesion; D015815:Cell Adhesion Molecules / Q000737:chemistry / Q000378:metabolism*; D002465:Cell Movement; D019281:Dimerization; D000939:Epitopes / Q000378:metabolism; D005353:Fibronectins / Q000378:metabolism; D006801:Humans; D039441:Integrin alpha4; D051379:Mice; D008807:Mice, Inbred BALB C; D016297:Mutagenesis, Site-Directed; D014162:Transfection
D015703:Antigens, CD; D015815:Cell Adhesion Molecules; D000939:Epitopes; D005353:Fibronectins; D039441:Integrin alpha4; D001224:Aspartic Acid