Bringing the Ca ²⁺ sensitivity of myristoylated recoverin into the physiological range

Abstract

The prototypical Ca 2+ -sensor protein recoverin (Rec) is thought to regulate the activity of rhodopsin kinase (GRK1) in photoreceptors by switching from a relaxed (R) disc membrane-bound conformation in the dark to a more compact, cytosol-diffusing tense (T) conformation upon cell illumination. However, the apparent affinity for Ca 2+ of its physiologically relevant form (myristoylated recoverin) is almost two orders of magnitude too low to support this mechanism in vivo . In this work, we compared the individual and synergistic roles of the myristic moiety, the GRK1 target and the disc membrane in modulating the calcium sensitivity of Rec. We show that the sole presence of the target or the disc membrane alone are not sufficient to achieve a physiological response to changes in intracellular [Ca 2+ ]. Instead, the simultaneous presence of GRK1 and membrane allows the T to R transition to occur in a physiological range of [Ca 2+ ] with high cooperativity via a conformational selection mechanism that drives the structural transitions of Rec in the presence of multiple ligands. Our conclusions may apply to other sensory transduction systems involving protein complexes and biological membranes.

A hybrid stochastic/deterministic model of single photon response and light adaptation in mouse rods

“…The regulation of rhodopsin phosphorylation by a Ca 2+ -feedback on rhodopsin kinase is crucial for shutting off the phototransduction cascade. The feedback is operated by recoverin that, in its myristoylated form, can switch between functionally distinct states in the presence of disc membrane and rhodopsin kinase [45] . We investigated the effect of removing this feedback mechanism in the DM, and deleted the mechanism when splitting the model into a stochastic frontend and a deterministic backend for the stochastic simulations.…”

Calcium- and Integrin-Binding Protein 2 (CIB2) in Physiology and Disease: Bright and Dark Sides

“…The presence of physiological targets is known to significantly tune the metal affinity of Ca 2+ sensors, often increasing it, such as in the case of myristoylated recoverin, a prototypical NCS protein in which the co-presence of the GRK1 target and the membrane is required to bring the Ca 2+ sensitivity into the physiological range, thus enhancing over 100-fold the apparent Ca 2+ affinity with respect to the isolated protein [ 33 ]. In the case of CIB2, the presence of a membrane-proximal peptide from the cytoplasmic domain of the α7B integrin was shown to double the apparent affinity for Ca 2+ (K d app = 200 μM vs. 500 μM in the absence of the target) [ 14 ].…”