Generation of a minimal alpha(5)beta(1) integrin-Fc fragment

The tertiary structure of the integrin heterodimer is currently unknown, al though several predictive models have been generated. Detailed structural s tudies of integrins have been consistently hampered for several reasons, in cluding the small amounts of purified protein available, the large size and conformational flexibility of integrins, and the presence of transmembrane domains and N-linked glycosylation sites in both receptor subunits. As a f irst step toward obtaining crystals of an integrin receptor, we have expres sed a minimized dimer. By using the Fc dimerization and mammalian cell expr ession system designed and optimized by Stephens et al. (Stephens, P. E., O rtlepp, S., Perkins, V. C., Robinson, M. K., and Kirby, H. (2000) Cell. Adh es. Commun. 7, 377-390), a series of recombinant soluble human alpha (5)bet a (1) integrin truncations have been expressed as Fc fusion proteins. These proteins were examined for their ligand-binding properties and for their e xpression of anti-integrin antibody epitopes. The shortest functional alpha (5)-subunit truncation contained the N-terminal 613 residues, whereas the shortest beta (1)-subunit was a fragment containing residues 121-455. Each of these minimally truncated integrins displayed the antibody binding chara cteristics of alpha (5)beta (1) purified from human placenta and bound liga nd with the same apparent affinity as the native receptor.