Distinct Structural Requirements for Interaction of the Integrins α5β1, αvβ5, and αvβ6 with the Central Cell Binding Domain in Fibronectin

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Abstract
At least 10 different members of the integrin family have been reported to bind to fibronectin, and eight of these interact with the arginine-glycine-aspartic acid (RGD) site in the tenth type III repeat. However, studies utilizing recombinant fibronectin fragments have shown that for three of these, α5β1, αIIbβ3, and αvβ3, the structural requirements for binding to fibronectin differ. In the present study. we report that two additional integrins, αvβ6. and αvβ5 also demonstrate unique requirements for interaction with recombinant fibronectin fragments. αvβ5, like αvβ3, can support cell adhesion to the RGD-containing tenth repeat alone, and does not require the presence of a synergy site in the adjacent ninth repeat. In the cells used in this study. αvβ5 only minimally supported adhesion to intact fibronectin. but did support adhesion to fragments composed of the eighth, ninth and tenth repeats or the tenth repeat. alone. Mutant fragments in which the eighth and tenth repeats were adjacent to one another enhanced adhesion mediated by αvβ5, as well as adhesion mediated by αvβ6. αvβ5 and αvβ6-mediated adhesion to all fibronectin fragments required interaction with the RGD site, as inferred by inhibition of adhesion with an RGD-containing peptide. These data suggest that each integrin that interacts with the RGD site in fibronectin has unique structural requirements for this interaction.

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