Analysis of the movements of helices in EF‐hands

We have developed a method to place an EF‐lobe in a coordinate system that recognizes the similarity of its two EF‐hand domains as well as their relationship by a pseudo‐two fold axis, z. The x‐axis connects the center of mass, calculated from α‐carbons of helices E1 and F1, with the center of mass of E2 and F2. The resulting coordinate system is intrinsic to each EF‐lobe and requires no comparison with other EF‐lobes. It has provided an intuitive and informative way to compare EF‐lobes and especially those changes associated with calcium and/or target binding. We analyzed the EF‐lobes of calmodulin and of other subfamilies with four EF‐hands. We have rationalized a complex pattern of changes of conformation associated with calcium coordination and effector binding as observed in different subfamilies of EF‐hand proteins. Proteins 2012. © 2012 Wiley Periodicals, Inc.