Identification of Chromosomal HP0892-HP0893 Toxin-Antitoxin Proteins in Helicobacter pylori and Structural Elucidation of Their Protein-Protein Interaction
ABSTRACT Bacterial chromosomal toxin-antitoxin (TA) systems have been proposed not only to play an important role in the stress response, but also to be associated with antibiotic resistance. Here, we identified the chromosomal HP0892-HP0893 TA proteins in the gastric pathogen, Helicobacter pylori (H. pylori), and structurally characterized their protein-protein interaction. Previously, HP0892 protein was suggested to be a putative TA toxin based on its structural similarity to other RelE family TA toxins. In this study, we demonstrated that HP0892 binds to HP0893 strongly with a stoichiometry of 1:1 and HP0892-HP0893 interaction occurs mainly between the N-terminal secondary structure elements of HP0892 and the C-terminal region of HP0893. HP0892 cleaved mRNA in vitro, preferentially at 5 end of A or G, and the RNase activity of HP0892 was inhibited by HP0893. In addition, heterologous expression of HP0892 in E. coli cells led to cell growth arrest, and the cell toxicity of HP0892 was neutralized by co-expression with HP0893. From these results and a structural comparison with other TA toxins, it is concluded that HP0892 is a toxin with intrinsic RNase activity and HP0893 is an antitoxin against HP0892 from a TA system of H. pylori. It has been known that hp0893 gene and another TA antitoxin gene, hp0895, of H. pylori, are both genomic open reading frames that correspond to genes that are potentially expressed in response to interactions with the human gastric mucosa. Therefore, it is highly probable that TA systems of H. pylori are involved in virulence of H. pylori.
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ABSTRACT: The toxin-antitoxin (TA) systems widely spread among bacteria and archaea are important for antibiotic resistance and microorganism virulence. The bacterial kingdom uses TA systems to adjust the global level of gene expression and translation through RNA degradation. In Helicobacter pylori, only two TA systems are known thus far. Our previous studies showed that HP0894-HP0895 acts as a TA system and that HP0894 exhibits intrinsic RNase activity. However, the precise molecular basis for interaction with substrate or antitoxin and the mechanism of mRNA cleavage remains unclear. Therefore, in an attempt to shed some light on the mechanism behind the TA system of HP0894-HP0895, here we present the crystal structures of apo- and metal-bound H. pylori 0894 at 1.28 Å and 1.89 Å, respectively. Through the combined approach of structural analysis and structural homology search, the amino acids involved in mRNase active site were monitored and the reorientations of different residues were discussed in detail. In the mRNase active site of HP0894 toxin, His84 acts as a catalytic residue and reorients itself to exhibit this type of activity, acting as a general acid in an acid-base catalysis reaction, while His47 and His60 stabilize the transition state. Lys52, Glu58, Asp64 and Arg80 have phosphate binding and specific sequence recognition. Glu58 also acts as a general base, and substrate reorientation is caused by Phe88. Based on experimental findings, a model for antitoxin binding could be suggested.Biochimica et Biophysica Acta 09/2013; 1834(12). DOI:10.1016/j.bbapap.2013.09.006 · 4.66 Impact Factor
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ABSTRACT: Due to the widespread and increasing appearance of antibiotic resistance, a new strategy is needed for developing novel antibiotics. Especially, there are no specific antibiotics for Helicobacter pylori (H. pylori). H. pylori are bacteria that live in the stomach and are related to many serious gastric problems such as peptic ulcers, chronic gastritis, mucosa-associated lymphoid tissue lymphoma, and gastric cancer. Because of its importance as a human pathogen, it's worth studying the structure and function of the proteins from H. pylori. After the sequencing of the H. pylori strain 26695 in 1997, more than 1,600 genes were identified from H. pylori. Until now, the structures of 334 proteins from H. pylori have been determined. Among them, 309 structures were determined by X-ray crystallography and 25 structures by Nuclear Magnetic Resonance (NMR), respectively. Overall, the structures of large proteins were determined by X-ray crystallography and those of small proteins by NMR. In our lab, we have studied the structural and functional characteristics of small proteins from H. pylori. In this review, 25 NMR structures of H. pylori proteins will be introduced and their structure-function relationships will be discussed.Molecules 11/2013; 18(11):13410-24. DOI:10.3390/molecules181113410 · 2.42 Impact Factor
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ABSTRACT: The Vibrio cholerae type VI secretion system (T6SS) assembles as a molecular syringe that injects toxic protein effectors into both eukaryotic and prokaryotic cells. We previously reported that the V. cholerae O37 serogroup strain V52 maintains a constitutively active T6SS to kill other Gram-negative bacteria while being immune to attack by kin bacteria. The pandemic O1 El Tor V. cholerae strain C6706 is T6SS-silent under laboratory conditions as it does not produce T6SS structural components and effectors, and fails to kill Escherichia coli prey. Yet, C6706 exhibits full resistance when approached by T6SS-active V52. These findings suggested that an active T6SS is not required for immunity against T6SS-mediated virulence. Here, we describe a dual expression profile of the T6SS immunity protein-encoding genes tsiV1, tsiV2, and tsiV3 that provides pandemic V. cholerae strains with T6SS immunity and allows T6SS-silent strains to maintain immunity against attacks by T6SS-active bacterial neighbors. The dual expression profile allows transcription of the three genes encoding immunity proteins independently of other T6SS proteins encoded within the same operon. One of these immunity proteins, TsiV2, protects against the T6SS effector VasX which is encoded immediately upstream of tsiV2. VasX is a secreted, lipid-binding protein that we previously characterized with respect to T6SS-mediated virulence towards the social amoeba Dictyostelium discoideum. Our data suggest the presence of an internal promoter in the open reading frame of vasX that drives expression of the downstream gene tsiV2. Furthermore, VasX is shown to act in conjunction with VasW, an accessory protein to VasX, to compromise the inner membrane of prokaryotic target cells. The dual regulatory profile of the T6SS immunity protein-encoding genes tsiV1, tsiV2, and tsiV3 permits V. cholerae to tightly control T6SS gene expression while maintaining immunity to T6SS activity.PLoS Pathogens 12/2013; 9(12):e1003752. DOI:10.1371/journal.ppat.1003752 · 8.06 Impact Factor