RESUMO
The anaerobic bacterium Chrysiogenes arsenatis respires using the oxyanion arsenate (AsO43-) as the terminal electron acceptor, where it is reduced to arsenite (AsO33-) while concomitantly oxidizing various organic (e.g., acetate) electron donors. This respiratory activity is catalyzed in the periplasm of the bacterium by the enzyme arsenate reductase (Arr), with expression of the enzyme controlled by a sensor histidine kinase (ArrS) and a periplasmic-binding protein (PBP), ArrX. Here, we report for the first time, the molecular structure of ArrX in the absence and presence of bound ligand arsenate. Comparison of the ligand-bound structure of ArrX with other PBPs shows a high level of conservation of critical residues for ligand binding by these proteins; however, this suite of PBPs shows different structural alterations upon ligand binding. For ArrX and its homologue AioX (from Rhizobium sp. str. NT-26), which specifically binds arsenite, the structures of the substrate-binding sites in the vicinity of a conserved and critical cysteine residue contribute to the discrimination of binding for these chemically similar ligands.
Assuntos
Arseniato Redutases/química , Bactérias/metabolismo , Sequência de Aminoácidos/genética , Arseniato Redutases/metabolismo , Arseniatos/química , Arseniatos/metabolismo , Bactérias/química , Composição de Bases/genética , Sítios de Ligação , Catálise , Cristalografia por Raios X/métodos , Histidina Quinase/metabolismo , Oxirredutases/metabolismo , Periplasma/metabolismo , Proteínas Periplásmicas de Ligação/química , Proteínas Periplásmicas de Ligação/metabolismo , Filogenia , RNA Ribossômico 16S/genética , Análise de Sequência de DNA/métodosRESUMO
Grx1, a cytosolic thiol-disulfide oxidoreductase, actively maintains cellular redox homeostasis using glutathione substrates (reduced, GSH, and oxidized, GSSG). Here, the crystallization of reduced Grx1 from the yeast Saccharomyces cerevisiae (yGrx1) in space group P212121 and its structure solution and refinement to 1.22â Å resolution are reported. To study the structure-function relationship of yeast Grx1, the crystal structure of reduced yGrx1 was compared with the existing structures of the oxidized and glutathionylated forms. These comparisons revealed structural differences in the conformations of residues neighbouring the Cys27-Cys30 active site which accompany alterations in the redox status of the protein.