Molecular Recognition of Rhodopsin Kinase GRK1 and Recoverin Is Tuned by Switching Intra- and Intermolecular Electrostatic Interactions.

G protein-coupled receptor kinase 1 (GRK1) or rhodopsin kinase is under specific control of the neuronal Ca2+-sensor protein recoverin, which is a critical feedback mechanism responsible for the modulation of the shape and sensitivity of the rod cell photoresponse. This process requires the precise matching of interacting protein surfaces and the dynamic changes in protein conformations. Here we study the molecular recognition process of recoverin and GRK1 by testing the hypothesis of a cation-π interaction pair in the recoverin-GRK1 complex. The critical role of residue K192 in recoverin was investigated by site-directed mutagenesis and subsequent structural and functional analysis. The following methods were used: isothermal titration calorimetry, fluorescence and circular dichroism spectroscopy, Ca2+-dependent membrane binding, and protein-protein interaction analysis by back scattering interferometry and surface plasmon resonance. While neutralizing the charge at K in the mutant K192L did not prevent binding of recoverin to GRK1, reversing the charge from K to E led to more distortions in the interaction process, but both mutations increased the stability of the protein conformation. Molecular dynamics simulations provided an explanation for these findings as they let us suggest that residue 192 per se is not a major stabilizer of the interaction between recoverin and its target but rather that the native K is involved in a network of switching electrostatic interactions in wild-type recoverin.