title: Atypical response regulator ChxR from Chlamydia trachomatis is structurally poised for DNA binding.
abstract: ChxR is an atypical two-component signal transduction response regulator (RR) of the OmpR/PhoB subfamily encoded by the obligate intracellular bacterial pathogen Chlamydia trachomatis. Despite structural homology within both receiver and effector domains to prototypical subfamily members, ChxR does not require phosphorylation for dimer formation, DNA binding or transcriptional activation. Thus, we hypothesized that ChxR is in a conformation optimal for DNA binding with limited interdomain interactions. To address this hypothesis, the NMR solution structure of the ChxR effector domain was determined and used in combination with the previously reported ChxR receiver domain structure to generate a full-length dimer model based upon SAXS analysis. Small-angle scattering of ChxR supported a dimer with minimal interdomain interactions and effector domains in a conformation that appears to require only subtle reorientation for optimal major/minor groove DNA interactions. SAXS modeling also supported that the effector domains were in a head-to-tail conformation, consistent with ChxR recognizing tandem DNA repeats. The effector domain structure was leveraged to identify key residues that were critical for maintaining protein - nucleic acid interactions. In combination with prior analysis of the essential location of specific nucleotides for ChxR recognition of DNA, a model of the full-length ChxR dimer bound to its cognate cis-acting element was generated.
authors.affiliation: Department of Molecular Biosciences, University of Kansas, Lawrence, Kansas, United States of America.
authors.forename: Michael L
authors.initials: ML
authors.lastname: Barta
authors.affiliation: Department of Pharmaceutical Chemistry, University of Kansas, Lawrence, Kansas, United States of America.
authors.forename: John M
authors.initials: JM
authors.lastname: Hickey
authors.affiliation: Del Shankel Structural Biology Center, University of Kansas, Lawrence, Kansas, United States of America.
authors.forename: Asokan
authors.initials: A
authors.lastname: Anbanandam
authors.affiliation: Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States of America.
authors.forename: Kevin
authors.initials: K
authors.lastname: Dyer
authors.affiliation: Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States of America.
authors.forename: Michal
authors.initials: M
authors.lastname: Hammel
authors.affiliation: Department of Molecular Biosciences, University of Kansas, Lawrence, Kansas, United States of America.
authors.forename: P Scott
authors.initials: PS
authors.lastname: Hefty
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002692:Chlamydia trachomatis / Q000235:genetics / Q000378:metabolism*; D004269:DNA, Bacterial / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D015964:Gene Expression Regulation, Bacterial; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D055503:Protein Multimerization; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D020080:Tandem Repeat Sequences; D013816:Thermodynamics
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D011994:Recombinant Proteins