Abstract
Two-component signal transduction systems, commonly found in prokaryotes, typically regulate cellular functions in response to environmental conditions through a phosphorylation-dependent process. A new type of response regulator, hp1043 (HP-RR) from Helicobacter pylori, has been recently identified. HP-RR is essential for cell growth and does not require the well known phosphorelay scheme. Unphosphorylated HP-RR binds specifically to its own promoter (P(1043)) and autoregulates the promoter of the tlpB gene (P(tlpB)). We have determined the structure of HP-RR by NMR and x-ray crystallography, revealing a symmetrical dimer with two functional domains. The molecular topology resembles that of the OmpR/PhoB subfamily, however, the symmetrical dimer is stable even in the unphosphorylated state. The dimer interface, formed by three secondary structure elements (alpha4-beta5-alpha5), resembles that of the active, phosphorylated forms of ArcA and PhoB. Several conserved residues of the HP-RR dimeric interface deviate from the OmpR/PhoB subfamily, although there are similar salt bridges and hydrophobic patches within the interface. Our findings reveal how a new type of response regulator protein could function as a cell growth-associated regulator in the absence of post-translational modification.
Highlights
Two-component systems are the predominant signal transduction systems used by prokaryotes and are frequently involved in the regulation of cellular functions in response to variable environmental conditions
Characterization of DNA Binding of HP-regulator protein (RR)—A recent report proposed that unphosphorylated HP-RR binds to a 29-mer target DNA containing its own promoter sequence [13], which is dependent upon the growth phase at the posttranscriptional level
HP-RR does not have the conserved phosphorylation site corresponding to Asp57 in E. coli CheY and avidly binds its own promoter sequence without phosphorylation
Summary
Disallowed regions a Two restraints per one hydrogen bond. b Root mean square deviation values for residues 1–115 for HP-RRr and 119 –218 for HP-RRc. c R-factor ϭ ⌺ʈFo ϪFcʈ/⌺͉Fo, whereFoandFcare the observed and calculated structure factor amplitudes, respectively. A recent report revealed that the regulatory domain (HP-RRr) is not phosphorylated in vitro and phosphorylation is not necessary for its function, indicating that HP-RR differs from the well known two-component response regulators. A recent report showed that PhoB adopts two different dimerization modes: the inactive ␣1-␣5 interface dimer and the active ␣4-5-␣5 interface dimer [17] These reports raise questions about the structure-function relationships of HP-RR related to dimerization and activation. We have reported preliminary NMR data showing that HP-RR is a symmetric dimer with two functional domains, an N-terminal regulatory domain (ϳ14 kDa) and C-terminal DNA-binding/transactivation domain (ϳ11 kDa) [18]. The structural information presented here will promote understanding of the molecular function of this new type of response regulator.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
