title: Nuclear magnetic resonance structure and dynamics of the response regulator Sma0114 from Sinorhizobium meliloti.
abstract: Receiver domains control intracellular responses triggered by signal transduction in bacterial two-component systems. Here, we report the solution nuclear magnetic resonance structure and dynamics of Sma0114 from the bacterium Sinorhizobium meliloti, the first such characterization of a receiver domain from the HWE-kinase family of two-component systems. The structure of Sma0114 adopts a prototypical α(5)/β(5) Rossman fold but has features that set it apart from other receiver domains. The fourth β-strand of Sma0114 houses a PFxFATGY sequence motif, common to many HWE-kinase-associated receiver domains. This sequence motif in Sma0114 may substitute for the conserved Y-T coupling mechanism, which propagates conformational transitions in the 455 (α4-β5-α5) faces of receiver domains, to prime them for binding downstream effectors once they become activated by phosphorylation. In addition, the fourth α-helix of the consensus 455 face in Sma0114 is replaced with a segment that shows high flexibility on the pico- to nanosecond time scale by (15)N relaxation data. Secondary structure prediction analysis suggests that the absence of helix α4 may be a conserved property of the HWE-kinase-associated family of receiver domains to which Sma0114 belongs. In spite of these differences, Sma0114 has a conserved active site, binds divalent metal ions such as Mg(2+) and Ca(2+) that are required for phosphorylation, and exhibits micro- to millisecond active-site dynamics similar to those of other receiver domains. Taken together, our results suggest that Sma0114 has a conserved active site but differs from typical receiver domains in the structure of the 455 face that is used to effect signal transduction following activation.
authors.affiliation: Department of Molecular and Cellular Biology, University of Connecticut, Storrs, CT 06269, USA.
authors.forename: Sarah R
authors.initials: SR
authors.lastname: Sheftic
authors.forename: Preston P
authors.initials: PP
authors.lastname: Garcia
authors.forename: Emma
authors.initials: E
authors.lastname: White
authors.forename: Victoria L
authors.initials: VL
authors.lastname: Robinson
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Gage
authors.forename: Andrei T
authors.initials: AT
authors.lastname: Alexandrescu
mesh_terms: D002118:Calcium / Q000378:metabolism; D020134:Catalytic Domain; D000071677:Histidine Kinase; D008274:Magnesium / Q000378:metabolism; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D010802:Phylogeny; D011487:Protein Conformation; D017510:Protein Folding; D011494:Protein Kinases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D016962:Sinorhizobium meliloti / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism
chemical_list: D011494:Protein Kinases; D000071677:Histidine Kinase; D008274:Magnesium; D002118:Calcium