THE ALPHA-1-BETA-1-INTEGRIN RECOGNITION SITE OF THE BASEMENT-MEMBRANE COLLAGEN MOLECULE [ALPHA-1(IV)](2)ALPHA-2(IV)

Cells interact with type IV collagen mainly via the integrins alpha1beta1 and alpha2beta1. A triple helical CNBr derived fragment CB3[IV], which contains the recognition sites for both integrins, was isolated from type IV collagen. Trypsin treatment of CB3[IV] gave rise to four smaller fragments, F1-F4, of which the smallest one, F4, contained the recognition site for alpha1beta1. Further fragmentation of F4 by thermolysin treatment at 50-degrees-C led to fragment TL1, which represents the C-terminal half of F4, and which was no longer able to interact with alpha1beta1. Therefore the recognition site of alpha1beta1 had to be located within the N-terminal half of F4, a position which was verified by electron micrographs of a crosslinked F2-alpha1beta1 complex. Modification of the Arg and Asp residues, which abolished the binding activity of F4, led to the identification of Arg (461) within the alpha2(IV) and Asp (461) within the alpha1(IV) chain as essential residues for the alpha1beta1. The array of these two residues on the surface of the triple helix is discussed.