title: Hypothetical protein CT398 (CdsZ) interacts with σ(54) (RpoN)-holoenzyme and the type III secretion export apparatus in Chlamydia trachomatis.
abstract: A significant challenge to bacteriology is the relatively large proportion of proteins that lack sufficient sequence similarity to support functional annotation (i.e. hypothetical proteins). The aim of this study was to apply protein structural homology to gain insights into a candidate protein of unknown function (CT398) within the medically important, obligate intracellular bacterium Chlamydia trachomatis. C. trachomatis is a major human pathogen responsible for numerous infections throughout the world that can lead to blindness and infertility. A 2.12 Å crystal structure of hypothetical protein CT398 was determined that was comprised of N-terminal coiled-coil and C-terminal Zn-ribbon domains. The structure of CT398 displayed a high degree of structural similarity to FlgZ (Flagellar-associated zinc-ribbon domain protein) from Helicobacter pylori. This observation directed analyses of candidate protein partners of CT398, revealing interactions with two paralogous type III secretion system (T3SS) ATPase-regulators (CdsL and FliH) and the alternative sigma factor RpoN (σ(54) ). Furthermore, genetic introduction of a conditional expression, affinity-tagged construct into C. trachomatis enabled the purification of a CT398-RpoN-holoenzyme complex, suggesting a potential role for CT398 in modulating transcriptional activity during infection. The interactions reported here, in tandem with previous FlgZ studies in H. pylori, indicate that CT398 functions as a regulator of several key areas of chlamydial biology throughout the developmental cycle. Accordingly, we propose that CT398 be named CdsZ (Contact-dependent secretion-associated zinc-ribbon domain protein).
authors.affiliation: Department of Molecular Biosciences, University of Kansas, Lawrence, KS, 66045.
authors.forename: Michael L
authors.initials: ML
authors.lastname: Barta
authors.affiliation: IMCA-CAT, Hauptman-Woodward Medical Research Institute, Argonne, Illinois.
authors.forename: Kevin P
authors.initials: KP
authors.lastname: Battaile
authors.affiliation: Protein Structure Laboratory, Del Shankel Structural Biology Center, University of Kansas, Lawrence, KS, 66045.
authors.forename: Scott
authors.initials: S
authors.lastname: Lovell
authors.affiliation: Department of Molecular Biosciences, University of Kansas, Lawrence, KS, 66045.
authors.forename: P Scott
authors.initials: PS
authors.lastname: Hefty
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D002692:Chlamydia trachomatis / Q000737:chemistry* / Q000378:metabolism*; D003198:Computer Simulation; D012321:DNA-Directed RNA Polymerases / Q000737:chemistry; D020035:Holoenzymes / Q000737:chemistry / Q000378:metabolism*; D008954:Models, Biological; D008958:Models, Molecular; D051877:RNA Polymerase Sigma 54 / Q000737:chemistry*; D016415:Sequence Alignment; D012808:Sigma Factor / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; D020035:Holoenzymes; D012808:Sigma Factor; D012321:DNA-Directed RNA Polymerases; D051877:RNA Polymerase Sigma 54
keywords: Chlamydia; Zn-ribbon; coiled-coil; structural proteomics; type III secretion system