title: 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 Mycoplasma pneumoniae and M. capricolum have molecular masses of 11-2 and 12 kDa, respectively, and are stable at 90 degree C for 10 min. Both TRXs reacted with monospecific polyclonal antibodies 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 election donor, a requirement which could not be fulfilled by NADH. The genes encoding the TRX and NTR (trxA and trxB) or 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 at 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.
authors.affiliation: Department of Membrane and Ultrastructure Research, The Hebrew University-Hadassah Medical School, POB 12272, Jerusalem 91120, Israel.
authors.forename: G
authors.initials: G
authors.lastname: Ben-Menachem
authors.affiliation: Department of Microbiology, University of Heidelberg, Im Neuenheimer Feld 282, D-6900 Heidelberg, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Himmelreich
authors.affiliation: Department of Microbiology, University of Heidelberg, Im Neuenheimer Feld 282, D-6900 Heidelberg, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Herrmann
authors.affiliation: Department of Molecular Microbiology and Biotechnology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv 69978, Israel.
authors.forename: Y
authors.initials: Y
authors.lastname: Aharonowitz
authors.affiliation: Department of Membrane and Ultrastructure Research, The Hebrew University-Hadassah Medical School, POB 12272, Jerusalem 91120, Israel.
authors.forename: S
authors.initials: S
authors.lastname: Rottem
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D001483:Base Sequence / Q000235:genetics; D003001:Cloning, Molecular; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009174:Mycoplasma / Q000737:chemistry / Q000201:enzymology*; D010084:Oxidation-Reduction; D017386:Sequence Homology, Amino Acid; D008973:Tenericutes / Q000201:enzymology / Q000254:growth & development; D013880:Thioredoxin-Disulfide Reductase / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology*; D013879:Thioredoxins / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D013879:Thioredoxins; D013880:Thioredoxin-Disulfide Reductase