MOLECULAR-IDENTIFICATION OF THE RYANODINE RECEPTOR CA2+ SENSOR

We have investigated the molecular basis for ryanodine receptor (RyR) activation by Ca2+ by using site-directed mutagenesis together with fu nctional assays consisting of Ca2+ release measurements and single cha nnel recordings in planar lipid bilayers, We report here that a single substitution of alanine for glutamate at position 3885 (located in th e putative transmembrane sequence M2 of the type 3 RyR) reduces the Ca 2+ sensitivity, as measured by single channel activation, by more than 10,000-fold, without apparent changes in channel conductance and in m odulation by other ligands (e.g. ATP and ryanodine). Co-expression of the wild type and mutant RyR proteins results in the synthesis of sing le channels that have intermediate Ca2+ sensitivities. These results s uggest that the glutamates at position 3885 of each monomer may act in a coordinated way to form the Ca2+ sensor in the tetrameric structure corresponding to RyR.