Re a widespread mechanism, which is initiated by hydride transfer from a pyridine nucleotide cofactor to flavin adenine dinucleotide (FAD), followed by delivery of reducing equivalents to a cysteine from the active web site disulfide and in the end for the substrate disulfide or, in the case of mercuric reductase, Hg+2.26 Figure five shows a various sequence alignment of Halobacterium sp. NRC-1 GCR and closely related putative GCRs from other XTP3TPA Protein site halobacteria with sequences of known pyridine nucleotide disulfide oxidoreductase family members, which includes glutathione reductases, mycothione reductases, trypanothione reductases, dihydrolipoylamide dehydrogenases, and mercuric reductases. (All of those proteins belong to PFAM household PF07992.) Conserved sequence motifs identified to interact together with the two cofactors, FAD and NADPH, are highlighted. The majority of the sequences also share the C-terminal dimerization domain having a signature HPT sequence. The exception would be the mercuric reductases, which have a distinctive C-terminal domain containing two cysteine residues which can be involved in binding Hg(II) at the active web-site. The many sequence alignment plus the conservation of various motifs in GCR support its inclusion within the pyridine nucleotide disulfide oxidoreductase family members.NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author ManuscriptDISCUSSIONLow molecular weight thiols serve many critical roles in cells. They act as redox buffers to keep the redox state of molecules in the cell. They lessen disulfide bonds triggered by oxidation of cellular thiols and react with alkylating reagents, as a result protecting DNA and proteins.27, 28 Thiols can serve as substrates in enzymatic reactions29, 30 and take part in regulation of CA125 Protein MedChemExpress protein function and cell signaling.31?three Despite the fact that the use of low molecularBiochemistry. Author manuscript; out there in PMC 2014 October 28.Kim and CopleyPageweight thiols for such purposes is typical, there is extraordinary diversity amongst the structures employed by unique evolutionary lineages (see Figure six).31, 32, 34, 35 Additional diversity is found within the enzymes that regenerate the thiols immediately after they may be oxidized. Most characterized thiol disulfide reductases, including glutathione reductase, trypanothione reductase, and mycothione reductase belong to the pyridine nucleotide disulfide oxidoreductase family members inside the two dinucleotide binding domains flavoproteins (tDBDF) superfamily26 and use either NADPH or NADH as a hydride donor. Within the case of ovothiol, which is found in sea urchin eggs36, the corresponding disulfide is decreased by glutathione as an alternative to a reductase protein. In protozoan parasites, ovothiol disulfide is usually decreased by trypanothione.37 Thus, numerous systems for working with thiols to defend against oxidative damage appear to possess evolved convergently in various lineages lengthy soon after the divergence from the LUCA in to the Bacterial, Archaeal and Eukaryal domains. Halobacteria are unique in their use of -Glu-Cys as a major low-molecular-weight thiol.38 We have previously postulated that the ability to create -Glu-Cys arose in halobacteria by means of horizontal gene transfer of a gene encoding -glutamyl cysteine ligase (GshA) from a cyanobacterium.39 Ordinarily, -Glu-Cys is converted to glutathione, the main thiol identified in eukaryotes and Gram-negative bacteria, by glutathione synthetase. -Glu-Cys lacks the glycine residue that is definitely present in glutathione. This discrepancy may be related to the highsalt content material in the Halobacterium cytoplasm. Cys.
