The prototypical Ca²⁺-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 Ca²⁺ 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 [Ca²⁺]. Instead, the simultaneous presence of GRK1 and membrane allows the T to R transition to occur in a physiological range of [Ca²⁺] 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.

原型 Ca ²⁺传感器蛋白恢复蛋白 (Rec) 被认为通过从黑暗中松弛的 (R) 圆盘膜结合构象转换为更紧凑的细胞溶质扩散构象来调节光感受器中视紫红质激酶 (GRK1) 的活性细胞光照时的紧张 (T) 构象。然而，对其生理相关形式（肉豆蔻酰化恢复蛋白）的Ca ²⁺的表观亲和力几乎低了两个数量级，无法在体内支持这种机制. 在这项工作中，我们比较了肉豆蔻部分、GRK1 靶标和椎间盘膜在调节 Rec 钙敏感性方面的个体和协同作用。我们表明，单独存在的目标或椎间盘膜不足以实现对细胞内 [Ca ²⁺ ]变化的生理反应。相反，GRK1 和膜的同时存在允许在 [Ca ²⁺ ]的生理范围内通过构象选择机制以高协同性发生 T 到 R 转变，该机制在多个配体存在下驱动 Rec 的结构转变。我们的结论可能适用于其他涉及蛋白质复合物和生物膜的感觉转导系统。