Atomic basis for the species-specific inhibition of {alpha}V integrins by mAb 17E6 is revealed by the crystal structure of {alpha}V{beta}3 ectodomain-17E6 Fab complex [Molecular Bases of Disease]

April 1st, 2014 by Mahalingam, B., Van Agthoven, J. F., Xiong, J.-P., Alonso, J. L., Adair, B. D., Rui, X., Anand, S., Mehrbod, M., Mofrad, M. R. K., Burger, C., Goodman, S. L., Arnaout, M. A.

The function-blocking, non-RGD containing and primate-specific mouse monoclonal antibody 17E6 binds the αV subfamily of integrins. 17E6 is currently in phase 2 clinical trials for treating cancer. To elucidate the structural basis of recognition and the molecular mechanism of inhibition, we crystallized αVβ3 ectodomain in complex with the Fab fragment of 17E6. Protein crystals grew in presence of the activating cation Mn2+. The integrin in the complex and in solution assumed the genuflected conformation. 17E6 Fab bound exclusively to the Propeller domain of the αV subunit. At the core of αV-Fab interface were interactions involving Propeller residues Lys203 and Gln145, the latter accounting for primate specificity. The Propeller residue Asp150, which normally coordinates Arg of the ligand Arg-Gly-Asp motif, formed contacts with Arg54 of the Fab that were expected to reduce soluble FN10 binding to cellular αVβ3 complexed with 17E6. This was confirmed in direct binding studies, suggesting that 17E6 is an allosteric inhibitor of αV integrins.
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