Structural differences among subfamilies of EF-hand proteins-A view from the pseudo two-fold symmetry axis

We have analyzed the conformations of EF-lobes, adjacent pairs of EF-hand domains, in a coordinate system based on the approximate two-fold (z) axis that relates the two EF-hands. Two parameters - dE(O), the azimuthal angle between the y-axis and the projection of the offset vector to helix E onto the yz-plane, and dF(O), the difference angle between the two helices (F1 and F2) of odd and even domainscharacterize the openness of a single EF-hand domain and of an EF-lobe, respectively. We describe and compare values of dE(O) and of dF(O) for EF-hand proteins of five subfamiliesCTER, CPV, S100, PARV, CALPin calci- and apo- forms, with and without bound target proteins. Each subfamily has characteristic changes associated with binding calcium and/or target proteins. Proteins 2014; 82:2915-2924. (c) 2014 Wiley Periodicals, Inc.