Legionella pneumophila utilizes a single-player disulfide-bond oxidoreductase system to manage disulfide bond formation and isomerization.

Legionella pneumophila uses a single homodimeric disulfide bond (DSB) oxidoreductase DsbA2 to catalyze extracytoplasmic protein folding and to correct DSB errors through protein-disulfide isomerase (PDI) activity. In Escherichia coli, these functions are separated to avoid futile cycling. In L. pneumophila, DsbA2 is maintained as a mixture of disulfides (S-S) and free thiols (SH), but when expressed in E. coli, only the SH form is observed. We provide evidence to suggest that structural differences in DsbB oxidases (LpDsbB1 and LpDsbB2) and DsbD reductases (LpDsbD1 and LpDsbD2) (compared with E. coli) permit bifunctional activities without creating a futile cycle. LpdsbB1 and LpdsbB2 partially complemented an EcdsbB mutant while neither LpdsbD1 nor LpdsbD2 complemented an EcdsbD mutant unless DsbA2 was also expressed. When the dsb genes of E. coli were replaced with those of L. pneumophila, motility was restored and DsbA2 was present as a mixture of redox forms. A dominant-negative approach to interfere with DsbA2 function in L. pneumophila determined that DSB oxidase activity was necessary for intracellular multiplication and assembly/function of the Dot/Icm Type IVb secretion system. Our studies show that a single-player system may escape the futile cycle trap by limiting transfer of reducing equivalents from LpDsbDs to DsbA2.

Disulfide bond oxidoreductase DsbA2 of Legionella pneumophila exhibits protein disulfide isomerase activity.

The extracytoplasmic assembly of the Dot/Icm type IVb secretion system (T4SS) of Legionella pneumophila is dependent on correct disulfide bond (DSB) formation catalyzed by a novel and essential disulfide bond oxidoreductase DsbA2 and not by DsbA1, a second nonessential DSB oxidoreductase. DsbA2, which is widely distributed in the microbial world, is phylogenetically distinct from the canonical DsbA oxidase and the DsbC protein disulfide isomerase (PDI)/reductase of Escherichia coli. Here we show that the extended N-terminal amino acid sequence of DsbA2 (relative to DsbA proteins) contains a highly conserved 27-amino-acid dimerization domain enabling the protein to form a homodimer. Complementation tests with E. coli mutants established that L. pneumophila dsbA1, but not the dsbA2 strain, restored motility to a dsbA mutant. In a protein-folding PDI detector assay, the dsbA2 strain, but not the dsbA1 strain, complemented a dsbC mutant of E. coli. Deletion of the dimerization domain sequences from DsbA2 produced the monomer (DsbA2N), which no longer exhibited PDI activity but complemented the E. coli dsbA mutant. PDI activity was demonstrated in vitro for DsbA2 but not DsbA1 in a nitrocefin-based mutant TEM ß-lactamase folding assay. In an insulin reduction assay, DsbA2N activity was intermediate between those of DsbA2 and DsbA1. In L. pneumophila, DsbA2 was maintained as a mixture of thiol and disulfide forms, while in E. coli, DsbA2 was present as the reduced thiol. Our studies suggest that DsbA2 is a naturally occurring bifunctional disulfide bond oxidoreductase that may be uniquely suited to the majority of intracellular bacterial pathogens expressing T4SSs as well as in many slow-growing soil and aquatic bacteria.

Disease phenotype and genotype are associated with shifts in intestinal-associated microbiota in inflammatory bowel diseases.

BACKGROUND: Abnormal host-microbe interactions are implicated in the pathogenesis of inflammatory bowel diseases. Previous 16S rRNA sequence analysis of intestinal tissues demonstrated that a subset of Crohn's disease (CD) and ulcerative colitis (UC) samples exhibited altered intestinal-associated microbial compositions characterized by depletion of Bacteroidetes and Firmicutes (particularly Clostridium taxa). We hypothesize that NOD2 and ATG16L1 risk alleles may be associated with these alterations. METHODS: To test this hypothesis, we genotyped 178 specimens collected from 35 CD, 35 UC, and 54 control patients for the three major NOD2 risk alleles (Leu 1007fs, R702W, and G908R) and the ATG16L1T300A risk allele, that had undergone previous 16S rRNA sequence analysis. Our statistical models incorporated the following independent variables: 1) disease phenotype (CD, UC, non-IBD control); 2) NOD2 composite genotype (NOD2(R) = at least one risk allele, NOD2(NR) = no risk alleles); 3) ATG16L1T300A genotype (ATG16L1(R/R), ATG16L1(R/NR), ATG16L1(NR/NR)); 4) patient age at time of surgery and all first-order interactions. The dependent variable(s) were the relative frequencies of bacterial taxa classified by applying the RDP 2.1 classifier to previously reported 16S rRNA sequence data. RESULTS: Disease phenotype, NOD2 composite genotype and ATG16L1 genotype were significantly associated with shifts in microbial compositions by nonparametric multivariate analysis of covariance (MANCOVA). Shifts in the relative frequencies of Faecalibacterium and Escherichia taxa were significantly associated with disease phenotype by nonparametric ANCOVA. CONCLUSIONS: These results support the concept that disease phenotype and genotype are associated with compositional changes in intestinal-associated microbiota.