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Publication Abstract from PubMed

We have analyzed the structure and function of the integrin alpha(1)I domain harboring a gain-of-function mutation E317A. To promote protein crystallization, a double variant with an additional C139S mutation was used. In cell adhesion assays, the E317A mutation promoted binding to collagen. Similarly, the double mutation C139S/E317A increased adhesion compared with C139S alone. Furthermore, soluble alpha(1)I C139S/E317A was a higher avidity collagen binder than alpha(1)I C139S, indicating that the double variant represents an activated form. The crystal structure of the activated variant of alpha(1)I was solved at 1.9 A resolution. The E317A mutation results in the unwinding of the alphaC helix, but the metal ion has moved toward loop 1, instead of loop 2 in the open alpha(2)I. Furthermore, unlike in the closed alphaI domains, the metal ion is pentacoordinated and, thus, prepared for ligand binding. Helix 7, which has moved downward in the open alpha(2)I structure, has not changed its position in the activated alpha(1)I variant. During the integrin activation, Glu(335) on helix 7 binds to the metal ion at the metal ion-dependent adhesion site (MIDAS) of the beta(1) subunit. Interestingly, in our cell adhesion assays E317A could activate collagen binding even after mutating Glu(335). This indicates that the stabilization of helix 7 into its downward position is not required if the alpha(1) MIDAS is already open. To conclude, the activated alpha(1)I domain represents a novel conformation of the alphaI domain, mimicking the structural state where the Arg(287)-Glu(317) ion pair has just broken during the integrin activation.

Structure of Collagen Receptor Integrin alpha1I Domain Carrying the Activating Mutation E317A.,Lahti M, Bligt E, Niskanen H, Parkash V, Brandt AM, Jokinen J, Patrikainen P, Kapyla J, Heino J, Salminen TA J Biol Chem. 2011 Dec 16;286(50):43343-51. Epub 2011 Oct 26. PMID:22030389^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.