title: Chlamydia abortus YhbZ, a truncated Obg family GTPase, associates with the Escherichia coli large ribosomal subunit.
abstract: The stringent stress response is vital for bacterial survival under adverse environmental conditions. Obligate intracellular Chlamydia lack key stringent response proteins, but nevertheless can interrupt the cell cycle and enter stasis or persistence upon amino acid starvation. A possible key protein retained is YhbZ, a homologue of the ObgE guanosine triphosphatase (GTPase) superfamily connecting the stringent stress response to ribosome maturation. Curiously, chlamydial YhbZ lacks the ObgE C-terminal domain thought to be essential for binding the large ribosomal subunit. We expressed recombinant Chlamydia abortus YhbZ and showed it to be a functional GTPase, with similar activity to other Obg GTPase family members. As Chlamydia are resistant to genetic manipulation, we performed heterologous expression and gradient centrifugation experiments in Escherichia coli and found that, despite the missing C-terminal domain, C. abortus YhbZ co-fractionates with the E. coli 50S large ribosomal subunit. In addition, overexpression of chlamydial YhbZ in E. coli leads to growth defects and elongation, as reported for other Obg members. YhbZ did not complement an E. coli obgE temperature-sensitive mutant, indicating the C-terminal acidic domain may have an additional role. This data supports a role for YhbZ linking the chlamydial stress response to ribosome function and cellular growth.
authors.affiliation: Institute of Veterinary Pathology, University of Zurich, Winterthurerstrasse 268, Zürich CH-8057, Switzerland. a.polkinghorne@qut.edu.au
authors.forename: Adam
authors.initials: A
authors.lastname: Polkinghorne
authors.forename: Lloyd
authors.initials: L
authors.lastname: Vaughan
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002689:Chlamydia / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D020559:Monomeric GTP-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D054658:Ribosome Subunits, Large / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment
chemical_list: D001426:Bacterial Proteins; D020559:Monomeric GTP-Binding Proteins