Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.9.3.1 (cytochrome oxidase)
 8,822 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The membrane-anchored thioredoxin-like protein (TlpA) from the Gram-negative soil bacterium Bradyrhizobium japonicum was initially discovered due to its essential role in the maturation of cytochrome aa3. A soluble form of TlpA lacking the N-terminal membrane anchor acts as a protein thiol:disulfide oxidoreductase. TlpA possesses an active-site disulfide bond common to all members of the thiol:disulfide oxidoreductase family. In addition, it contains two non-active-site cysteines that form a structural disulfide bond (Loferer, H., Bott, M., and Hennecke, H. (1993) EMBO J. 12, 3373-3383; Loferer, H., and Hennecke, H. (1994) Eur. J. Biochem. 223, 339-344). Here, we compare the far- and near-UV CD spectra of TlpA before and after reduction of both disulfides by dithiothreitol and show that the non-active-site disulfide bond is not required for the integrity of TlpA's native conformation. In contrast to dithiothreitol, reduced glutathione (GSH) selectively reduces the active-site disulfide and leaves the non-active-site disulfide bond intact, even at high molar excess over TlpA. The selective reduction of the active-site disulfide bond leads to a 10-fold increase of the intrinsic tryptophan fluorescence of TlpA at 355 nm, which may be interpreted as a quenching of tryptophan fluorescence by the active-site disulfide bond. Using the specific fluorescence of TlpA as a measure of its redox state, a value of 1.9 +/- 0.2 M was determined for the TlpA:glutathione equilibrium constant at pH 7.0, demonstrating that TlpA is a reductant, like cytoplasmic thioredoxins. The DsbA protein, which acts as the final oxidant of periplasmic secretory proteins in Escherichia coli, is not capable of oxidizing the active-site cysteines of TlpA. This suggests that TlpA's primary role in vivo is keeping the thiols of certain proteins reduced and that TlpA's active, reduced state may be maintained owing to its kinetically restricted oxidation by other periplasmic disulfide oxidoreductases such as DsbA.
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PMID:A bacterial thioredoxin-like protein that is exposed to the periplasm has redox properties comparable with those of cytoplasmic thioredoxins. 759 22

We report the discovery of a bacterial gene, tlpA, that codes for a hitherto unknown type of thioredoxin-like protein. The gene was found in the course of studying a Tn5 insertion mutant of the soybean root nodule symbiont Bradyrhizobium japonicum. The TlpA protein shared up to 31% amino acid sequence identity with various eukaryotic and prokaryotic thioredoxins and protein disulfide isomerases, and possessed a characteristic active-site sequence, Trp-Cys-Val-Pro-Cys. In contrast to all members of the thioredoxin family known to date, TlpA was shown to be anchored to the cytoplasmic membrane by means of an N-terminal transmembrane domain, while the active site-containing part of the protein faced the periplasm. The tlpA mutant had a pleiotropic phenotype in that it was defective in the development of a nitrogen fixing endosymbiosis and exhibited a strongly decreased oxidase activity, as compared with the wild-type. Holocytochrome aa3 was spectroscopically undetectable in the mutant, whereas the apoprotein of subunit one (CoxA) of this oxidase was still synthesized and incorporated into the cytoplasmic membrane. Since cytochrome aa3 is not a prerequisite for the development of symbiosis, the results suggest that TlpA is involved in at least two independent cellular processes, one of which is an essential periplasmic step in the maturation of cytochrome aa3.
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PMID:Bradyrhizobium japonicum TlpA, a novel membrane-anchored thioredoxin-like protein involved in the biogenesis of cytochrome aa3 and development of symbiosis. 825 65

TlpA, the membrane-anchored, thioredoxin-like protein from Bradyrhizobium japonicum, is essential for cytochrome aa3 biogenesis. The periplasmic domain of TlpA was previously shown to have protein thiol:disulfide oxidoreductase activity and reducing properties similar to those of cytoplasmic thioredoxins. Here, we replaced the proline-109 in its active-site sequence C107 V108 P109 C110 by a histidine residue. The resulting active-site motif (CVHC) resembles that of oxidizing thiol:disulfide oxidoreductases such as protein disulfide isomerase (PDI) and DsbA. Indeed, the TlpA variant P109H was by 66 mV more oxidizing than the wild-type protein. Nevertheless, the altered protein was even more efficient in catalyzing the reduction of insulin disulfides by dithiothreitol than the wild-type due to a faster recycling of its catalytically active, reduced form. Cells of B. japonicum expressing only the mutated tlpA gene had the same phenotypes as wild-type cells, suggesting that the change in the redox potential of TlpA was not critical for its in vivo function.
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PMID:Replacement of Pro109 by His in TlpA, a thioredoxin-like protein from Bradyrhizobium japonicum, alters its redox properties but not its in vivo functions. 913 95