NMR assignments for the Sinorhizobium meliloti response regulator Sma0114

Response regulators are terminal ends of bacterial two-component systems that undergo extensive structural reorganization in response to phosphoryl transfer from their cognate histidine kinases. The response regulator encoded by the gene sma0114 of Sinorhizobium meliloti is a part of a unique class of two-component systems that employ HWE histidine kinases. The distinct features of Sma0114 include a PFxFATGY motif that houses the conserved threonine in the “Y–T coupling” conformational switch which mediates output response through downstream protein–protein interactions, and the replacement of the conserved phenylalanine/tyrosine in Y–T coupling by a leucine. Here we present 1H, 15N, and 13C NMR assignments for Sma0114. We identify the secondary structure of the protein based on TALOS chemical shift analysis, 3JHNHα coupling constants and hydrogen–deuterium exchange. The secondary structure determined by NMR is in good agreement with that predicted from the sequence. Both methods suggest that Sma0114 differs from standard CheY-like folds by missing the fourth α-helix. Our initial NMR characterization of Sma0114 paves the way to a full investigation of the structure and dynamics of this response regulator.