Structural insights into human recoverin

Recoverin is a key calcium sensor that controls the desensitization of the visual rhodopsin by GRK1. Previous studies have traditionally been conducted on bovine protein (bRec), while data on human ortholog (hRec) remain scarce. Here, we combine X-ray crystallography, X-ray absorption spectroscopy (XANES), quantum mechanical calculations, molecular dynamics, and functional assays to provide an integrated characterization of hRec. The 2Ca 2+ -bound hRec structure was solved at 1.60 Å, showing that, unlike bRec, hRec interacts with ROS membranes at physiologically relevant submicromolar Ca 2+ levels, due to a species-specific charge distribution that might influence membrane interactions. Both recoverins form a set of Ca 2+ /Zn 2+ -bound conformers with improved functional performance. X-ray crystallography (1.85 Å) and XANES revealed a specific tetrahedral Zn 2+ site in 1Ca 2+ -bound hRec, the first such site reported in the NCS family. In 1Ca 2+ -bound hRec, zinc promotes the formation of active state, whereas in 2Ca 2+ -state of bRec, it significantly enhances GRK1 binding, as the latter can complement the Zn 2+ coordination. These data refine our understanding of recoverin function in humans and highlight its role as a key link between calcium and zinc signaling in mammalian photoreceptors under normal and pathological conditions.