The thioredoxin reductase system of mycoplasmas

Abstract

Representative species of the Mollicutes possess a thioredoxin reductase system (NTS) composed of a low-molecular-mass thioredoxin (TRX) and NADPH-binding thioredoxin reductase (NTR). The TRXs of Mycopkma pneumoniae and M. capricolum have molecular masses of 11-2 and 12 kDa, respectively, and are stable at 90 "C for 10 min. Both TRXs reacted with monospecif ic polyclonal anti bodies generated against the Bacillus subtilis TRX, but not with anti-Escherichia coli TRX antisera. The M. capricolum and M. pneumoniae NTRs were partially purified and were found to be active with the homologous TRX, but not with the TRX of B. subtilis or E. coli. The NTS activity had an optimal pH of 6-5-7-5 and was dependent on NADPH as an electron donor, a requirement which could not be fulfilled by NADH. The genes encoding the TRX and NTR (trxA and trxB) of M. pneumoniae were cloned and sequenced. The comparative analysis of the predicted amino acid sequence of trxA showed that the 11.2 kDa protein (102 aa) shared 26-68% sequence similarity with products of other known trxA genes and contained the conserved active site Cys-Gly-Pro-Cys. The predicted amino acid sequence of trxB contained 315 residues with a conserved NADPH binding domain and FAD binding domains I and II. The cysteine dithiol redox active region had isoleucine rather than threonine a t the active site, as compared with other NTRs. The high activity of the NTS in mycoplasmas suggests that mycoplasmas may have evolved the NTS to protect themselves from the consequences of their self-generated oxidative challenge.

Functional thioredoxin reductase from pathogenic and free-living Leptospira spp.

“…For LinTrxR and LbiTrxR1, under aerobic conditions, the peak at 450 nm decreased after addition of 100 μM NADPH, indicating the reduction of a flavin prosthetic group. These spectral behaviors are characteristic of NAD(P)H-dependent flavoreductases, and more specifically of TrxR [33,34]. Under identical experimental conditions LbiTrxR2 was insensible to the presence of NAD(P)H (no flavin reduction was observed), in agreement with results reported for TrxR from T. acidophilum [32].…”

Coinfection with Mycoplasma Pneumoniae and Chlamydia Pneumoniae in ruptured plaques associated with acute myocardial infarction

“…Epitopes of oxidized LDL are sufficiently antigenic to produce an inflammatory reaction in the arterial wall, suggesting a possible autoimmune reaction 53,54 . One characteristic of the mycoplasmas is the induction of oxidation 55 and formation of free radicals in the host cells and in the environment [56][57][58] ; antioxidation has a preventive effect against infection by mycoplasma 59 . When the cells are coinfected with a virus, an increase in the pathogenicity of both infectious agents occurs 60,61 .…”

Comparative Genome Analysis of “CandidatusPhytoplasma australiense” (Subgrouptuf-Australia I;rp-A) and “Ca. Phytoplasma asteris” Strains OY-M and AY-WB

“…Phytoplasma australiense" SpxA protein) that implied that spx was involved in the cell's response to thiol-specific oxidative (disulfide) stress (54). In mycoplasmas, the thioredoxin reductase system involving TrxA and TrxB is required by the pathogen for defense against reactive oxygen species such as hydrogen peroxide produced by the host (11,25,32). This system differs from those of other bacteria that encode catalases, peroxidases, and superoxide mutases to provide defense against oxidative stress (59,83).…”