Properties and function of the P type ion pumps cloned from Helicobacter pylori.

Three distinct P type pumps were cloned from H. pylori 69A. Two of these pumps, ATPase 439 and ATPase 948 (CopA), were isolated by gene library screening using DNA oligonucleotide primers. Amino acid similarities found for the predicted proteins were about 50% to Cd2+/Cu2+ pumps. Gene disruption mutagenesis rendered the H. pylori knockout mutants more sensitive to Zn2+ and Cd2+ (ATPase 439) or Cu2+ (CopA). Some of the ATPase 439-deficient mutants were negative for urease activity while the majority of the mutants remained positive. Functional diversity of the pumps was also reflected by the ion affinities found for N-terminal peptides of CopA to Cu2+ and of ATPase 439 to Ni2+, Cu2+ and CO2+. The membrane domain of the two pumps were experimentally shown to consist of eight membrane spans. When ATPase 439 was expressed under control of a tac promoter in Escherichia coli, vanadate-sensitive phosphate accumulation was observed cytochemically along the membrane of the host cells. The third P type pump (ATPase 115) which also exhibited homology to transition metal ATPase was identified by sequencing a library of H. pylori membrane genes. The hydropathy plot of this pump was very similar to the former H. pylori ATPases whereas the N-terminal ion binding region was distinct. It was concluded that, in H. pylori, the presence of three transition metal ATPases with distinct ion specificity contributes to the adaptive mechanisms for gastric survival.

A stable shuttle vector system for efficient genetic complementation of Helicobacter pylori strains by transformation and conjugation.

A versatile plasmid shuttle vector system was constructed, which is useful for genetic complementation of Helicobacter pylori strains or mutants with cloned genes of homologous or heterologous origin. The individual plasmid vectors consist of the minimal essential genetic elements, including an origin of replication for Escherichia coli, a H. pylori-specific replicon originally identified on a small cryptic H. pylori plasmid, an oriT sequence and a multiple cloning site. Shuttle plasmid pHel2 carries a chloramphenicol resistance cassette (catGC) and pHel3 contains a kanamycin resistance gene (aphA-3) as the selectable marker; both are functional in E. coli and H. pylori. The shuttle plasmids were introduced into the H. pylori strain P1 by natural transformation. A efficiency of 7.0 x 10(-7) and 4.7 x 10(-7) transformants per viable recipient was achieved with pHel2 and pHel3, respectively, and both vectors showed stable, autonomous replication in H. pylori. An approximately 100-fold higher H. pylori transformation rate was obtained when the shuttle vectors for transformation were isolated from the homologous H. pylori strain, rather than E. coli, indicating that DNA restriction and modification mechanisms play a crucial role in plasmid transformation. Interestingly, both shuttle vectors could also be mobilized efficiently from E. coli into different H. pylori recipients, with pHel2 showing an efficiency of 2.0 x 10(-5) transconjugants per viable H. pylori P1 recipient. Thus, DNA restriction seems to be strongly reduced or absent during conjugal transfer. The functional complementation of a recA-deficient H. pylori mutant by the cloned H. pylori recA+ gene, and the expression of the heterologous green fluorescent protein (GFP) in H. pylori demonstrate the general usefulness of this system, which will significantly facilitate the molecular analysis of H. pylori virulence factors in the future.

An improved TnMax mini-transposon system suitable for sequencing, shuttle mutagenesis and gene fusions.

A new collection of mini-transposons (mini-Tn) of the previously described TnMax series [Haas et al, Gene 130 (1993a) 23-31] has been constructed. The transposons (Tn) bear genes conferring resistance to either chloramphenicol (Cm) or kanamycin (Km). Each member of the new series (TnMax5-TnMax11) contains the general M13 forward (M13-FP) and reverse (M13-RP1) sequencing primers close to the inverted repeats (IR), facilitating the rapid and convenient determination of the DNA sequences flanking the transposon insertion site. Furthermore, the mini-Tn possess the infrequently occurring NotI sites, allowing the localization of genes on macro-restriction maps of bacterial species. Some derivatives contain promoterless trp-lacZ (TnMax11), xylE (TnMax10), phoA (TnMax6) or blaM (TnMax7, TnMax9) genes next to the IR, suitable for the generation of in vivo gene- and operon fusions to study gene regulation, protein export, or to determine the topology of proteins in bacterial membranes. A set of conjugative minimal plasmid vectors (pMin1, pMin2) are used to select for TnMax insertions into the cloned insert, rather than the vector sequences. Due to the small size of the mini-Tn, and a simple and efficient mutagenesis procedure, the TnMax system is a useful tool for targeting and sequencing of cloned genes in Escherichia coli, and especially for shuttle mutagenesis of bacterial species which cannot be targeted by direct transposition.

Genetic organization of a small cryptic plasmid of Helicobacter pylori.

A 2.9-kb cryptic plasmid of Helicobacter pylori (Hp), pHel1, was isolated and the complete nucleotide (nt) sequence was determined. An open reading frame (ORF1) was identified encoding a putative polypeptide of 63,709 Da, the existence and correct size of which was confirmed by T7 promoter expression analysis. The ORF1 sequence showed strong amino-acid sequence identity to a recently identified putative ORF1 protein of a cryptic Hp plasmid, pHPM180, and significant homologies to putative Rep proteins of Campylobacter coli (RepB) and Pediococcus halophilus (RepA), and was therefore designated RepA. A functional role of RepA in replication of pHel1 was demonstrated by the fact that only pHel1 plasmid derivatives with an intact repA gene were able to autonomously replicate in Hp. Upstream of repA, a 22-bp sequence was recognized which was tandemly repeated four and a half times, a feature typical for many replication origins (ori) and commonly termed a DNA iteron. Analysis of the repA upstream region by primer extension identified a transcription start point for the repA mRNA, but did not correspond to known consensus promoter sequences. Southern hybridizations using pHel1 as a probe under stringent conditions revealed that homologous sequences to pHel1 were present in nearly all plasmid-carrying Hp strains, but not in a plasmid-carrying Helicobacter felis strain, suggesting that this type of replicon is predominantly found in the Hp species.

Cloning of the Helicobacter pylori recA gene and functional characterization of its product.

The RecA protein is a key enzyme involved in DNA recombination in bacteria. Using a polymerase chain reaction (PCR) amplification we cloned a recA homolog from Helicobacter pylori. The gene revealed an open reading frame (ORF) encoding a putative protein of 37.6 kDa showing closest homology to the Campylobacter jejuni RecA (75.5% identity). A putative ribosome binding site and a near-consensus sigma 70 promoter sequence was found upstream of recA. A second ORF, encoding a putative protein with N-terminal sequence homology to prokaryotic and eukaryotic enolases, is located directly downstream of recA. Compared to the wild-type strains, isogenic H. pylori recA deletion mutants of strains 69A and NCTC11637 displayed increased sensitivity to ultraviolet light and abolished general homologous recombination. The recombinant H. pylori RecA protein produced in Escherichia coli strain GC6 (recA-) was 38 kDa in size but inactive in DNA repair, whereas the corresponding protein in H. pylori 69A migrated at the greater apparent molecular weight of approx. 40 kDa in SDS-polyacrylamide gels. However, complementation of the H. pylori mutant using the cloned recA gene on a shuttle vector resulted in a RecA protein of the original size and fully restored the general functions of the enzyme. These data can be best explained by a modification of RecA in H. pylori which is crucial for its function. The potential modification seems not to occur when the protein is produced in E. coli, giving rise to a smaller but inactive protein.

Purification and characterization of a sialidase from Clostridium chauvoei NC08596.

The sialidase secreted by Clostridium chauvoei NC08596 was purified to apparent homogeneity by ion-exchange chromatography, gel filtration, hydrophobic interaction-chromatography, FPLC ion-exchange chromatography, and FPLC gel filtration. The enzyme was enriched about 10,200-fold, reaching a final specific activity of 24.4 U mg-1. It has a relatively high molecular mass of 300 kDa and consists of two subunits each of 150 kDa. The cations Mn2+, Mg2+, and Ca2+ and bovine serum albumin have a positive effect on the sialidase activity, while Hg2+, Cu2+, and Zn2+, chelating agents and salt decrease enzyme activity. The substrate specificity, kinetic data, and pH optimum of the enzyme are similar to those of other bacterial sialidases.