Natural and Artificial Mutations in alpha IIb Integrin Lead to a Structural Deformation of a Calcium-Binding Site

作者：Mansour Wissam; Hauschner Hagit; Seligsohn Uri; Rosenberg Nurit; Einav Yulia^*

来源：Protein Journal, 2014, 33(5): 474-483.

DOI：10.1007/s10930-014-9579-5

• alpha IIb beta 3
• Calcium
• beta-Propeller
• Integrins

The platelet integrin alpha IIb beta 3 is widely accepted as a structural and a functional model of the broad integrin protein family. The four calcium-binding sites in the alpha IIb subunit contribute to biogenesis and stability of the protein. Mansour et al. (J Thromb Haemost 9:192-200, 2011) showed that the natural Asn2Asp mutation causing Glanzmann thrombasthenia, prevented surface expression of alpha IIb beta 3, whereas the artificial Asn2Gln mutation only decreased its level. Molecular dynamics simulations and EDTA chelation assay were used here to explore the mechanism of these structural deformations. We show a considerable expansion of the calcium-binding site 3 in Asn2Asp mutation, whereas the Asn2Gln toggles between normal and expanded conformations. The alpha IIb beta 3 surface expression level correlates to the relative spending time in the expanded conformation. By a comparison to other calcium-binding sites of alpha IIb and of other alpha integrins we show that the size of a calcium-binding loop is conserved. EDTA chelation assay shows a sensitivity to calcium removal, which correlates with the reduction in alpha IIb beta 3 surface expression and with the calcium binding site expansion, thus verifying the simulation data. Here we indicate that Asn2 mutation affects a calcium-binding site 3 of alpha IIb, which structural deformation is proposed to deprive calcium binding and interfere with an integrin intracellular trafficking and its surface expression.

• 出版日期2014-10