Similar but nonidentical amino acid results on vascular cell adhesion molecule-1 are involved in the interaction with alpha sub(4) beta sub(1) and alpha sub(4) beta sub(7) under different activity states

The integrin receptors alpha sub(4) beta sub(1) and alpha sub(4) beta sub(7) both bind to vascular cell adhesion molecule-1 (VCAM-1). Here, we report that the amino acid residue requirements for murine VCAM-1 adhesion to murine alpha sub(4) beta sub(1) (WEHI 231) and alpha sub(4) beta sub(7) (38C13/ beta 7-transfectant) positive cells are strikingly similar but nonidentical under multiple adhesion activity states. By site-directed mutagenesis of domain 1 of VCAM-1, the amino acid residues on the loop between beta strands C and D (R36, Q38, D40, P42) and on the adjacent antiparallel beta strand F (L70 and T72) were required for basal level adhesion to both alpha sub(4) beta sub(1)-positive and alpha sub(4) beta sub(7)-positive cells. Mutation at two other sites, N44 (loop between beta strands C and D) and E66 (loop between beta strands E and F), specifically reduced alpha sub(4) beta sub(7)-positive cell adhesion, but not alpha sub(4) beta sub(1)-positive cell adhesion. Mutation H85A augmented alpha sub(4) beta sub(7) binding but not alpha sub(4) beta sub(1) binding. These apparent differences relate to the higher intrinsic activity state of alpha sub(4) beta sub(1) on WEHI 231 than on alpha sub(4) beta sub(7) (38C13/ beta 7-transfectant). In contrast, under higher adhesion activity states induced by either MnCl sub(2) or truncation of the beta sub(7) cytoplasmic tail, mutation of their amino acid residue D40 or L70 completely blocked cell adhesion without evidence of structural perturbation of VCAM-1. These results suggested that the two structurally discontinuous amino acid residues, the negatively charged D40 and the hydrophobic L70 adjacently located on domain 1 of VCAM-1, are essential for interaction under multiple activity states with both alpha sub(4) beta sub(1) and alpha sub(4) beta sub(7) integrin receptors.