Conformational dynamics of recoverin's Ca 2+ ‐myristoyl switch probed by 15 N NMR relaxation dispersion and chemical shift analysis

Recoverin, a member of the neuronal calcium sensor (NCS) branch of the calmodulin superfamily, serves as a calcium sensor in retinal rod cells. Ca 2+ ‐induced conformational changes in recoverin promote extrusion of its covalently attached myristate, known as the Ca 2+ ‐myristoyl switch. Here, we present nuclear magnetic resonance (NMR) relaxation dispersion and chemical shift analysis on 15 N‐labeled recoverin to probe main chain conformational dynamics. 15 N NMR relaxation data suggest that Ca 2+ ‐free recoverin undergoes millisecond conformational dynamics at particular amide sites throughout the protein. The addition of trace Ca 2+ levels (0.05 equivalents) increases the number of residues that show detectable relaxation dispersion. The Ca 2+ ‐dependent chemical shifts and relaxation dispersion suggest that recoverin has an intermediate conformational state (I) between the sequestered apo state (T) and Ca 2+ saturated extruded state (R): T ↔ I ↔ R. The first step is a fast conformational equilibrium ([T]/[I] < 100) on the millisecond time scale (τ ex δω < 1). The final step (I ↔ R) is much slower (τ ex δω > 1). The main chain structure of I is similar in part to the structure of half‐saturated E85Q recoverin with a sequestered myristoyl group. We propose that millisecond dynamics during T ↔ I may transiently increase the exposure of Ca 2+ ‐binding sites to initiate Ca 2+ binding that drives extrusion of the myristoyl group during I ↔ R. Proteins 2011; © 2011 Wiley‐Liss, Inc.