Solution NMR structure of selenium-binding protein from Methanococcus vannielii.
ABSTRACT Selenium is an important nutrient. The lack of selenium will suppress expression of various enzymes that will lead to cell abnormality and diseases. However, high concentrations of free selenium are toxic to the cell because it adversely affects numerous cell metabolic pathways. In Methanococcus vannielii, selenium transport in the cell is established by the selenium-binding protein, SeBP. SeBP sequesters selenium during transport, thus regulating the level of free selenium in the cell, and delivers it specifically to the selenophosphate synthase enzyme. In solution, SeBP is an oligomer of 8.8-kDa subunits. It is a symmetric pentamer. The solution structure of SeBP was determined by NMR spectroscopy. Each subunit of SeBP is composed of an alpha-helix on top of a 4-stranded twisted beta-sheet. The stability of the five subunits stems mainly from hydrophobic interactions and supplemented by hydrogen bond interactions. The loop containing Cys(59) has been shown to be important for selenium binding, is flexible, and adopts multiple conformations. However, the cysteine accessibility is restricted in the structure, reducing the possibility of the binding of free selenium readily. Therefore, a different selenium precursor or other factors might be needed to facilitate opening of this loop to expose Cys(59) for selenium binding.
SourceAvailable from: Andrzej Joachimiak[Show abstract] [Hide abstract]
ABSTRACT: Bacterial species in the Enterobacteriaceae typically contain multiple paralogues of a small domain of unknown function (DUF1471) from a family of conserved proteins also known as YhcN or BhsA/McbA. Proteins containing DUF1471 may have a single or three copies of this domain. Representatives of this family have been demonstrated to play roles in several cellular processes including stress response, biofilm formation, and pathogenesis. We have conducted NMR and X-ray crystallographic studies of four DUF1471 domains from Salmonella representing three different paralogous DUF1471 subfamilies: SrfN, YahO, and SssB/YdgH (two of its three DUF1471 domains: the N-terminal domain I (residues 21-91), and the C-terminal domain III (residues 244-314)). Notably, SrfN has been shown to have a role in intracellular infection by Salmonella Typhimurium. These domains share less than 35% pairwise sequence identity. Structures of all four domains show a mixed α+β fold that is most similar to that of bacterial lipoprotein RcsF. However, all four DUF1471 sequences lack the redox sensitive cysteine residues essential for RcsF activity in a phospho-relay pathway, suggesting that DUF1471 domains perform a different function(s). SrfN forms a dimer in contrast to YahO and SssB domains I and III, which are monomers in solution. A putative binding site for oxyanions such as phosphate and sulfate was identified in SrfN, and an interaction between the SrfN dimer and sulfated polysaccharides was demonstrated, suggesting a direct role for this DUF1471 domain at the host-pathogen interface.PLoS ONE 07/2014; DOI:10.1371/journal.pone.0101787 · 3.53 Impact Factor
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ABSTRACT: The function of Selenium Binding Protein 1 (SBP1), present in almost all organisms, has not yet been established. In mammals, SBP1 is known to bind the essential element, Selenium but the binding site has not been identified. In addition, the SBP family has numerous potential metal binding sites that may play a role in detoxification pathways in plant. In Arabidopsis thaliana , SBP1 over-expression increases tolerance to two toxic compounds for plants, selenium and cadmium, often found as soil pollutants. For a better understanding of AtSBP1 function in detoxification mechanisms, we investigated the chelating properties of AtSBP1 towards different ligands with a focus on selenium using biochemical and biophysical techniques. Thermal - shift assay together with inductively coupled plasma mass spectrometry revealed that AtSBP1 binds selenium after incubation with selenite (SeO3 (2)) with a ligand to protein molar ratio of 1:1. Isothermal titration calorimetry confirmed the stoichiometry 1:1 and revealed an unexpectedly large value of binding enthalpy suggesting a covalent bond between selenium and AtSBP1. Titration of reduced Cys residues and comparative mass spectrometry on AtSBP1 and the purified selenium-AtSBP1 complex, identified Cys21 and Cys22 as being responsible for the binding of one selenium. These results were validated by site directed mutagenesis. Selenium K-edge X ray absorption near edge structure spectroscopy performed on the Selenium -AtSBP1 complex demonstrated that AtSBP1 reduced SeO3 (2-) to form a R-S-Se-S-R-type complex. The capacity of AtSBP1 to bind different metals and selenium is discussed with respect to the potential function of AtSBP1 in detoxification mechanisms and selenium metabolism.Journal of Biological Chemistry 10/2014; DOI:10.1074/jbc.M114.571208 · 4.60 Impact Factor
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ABSTRACT: Hepatocellular carcinoma (HCC) is one of the most lethal cancers in the world. Its etiology includes chronic liver disease, viral hepatitis, alcoholism, and hepatic cirrhosis. Both oxidative stress and inflammatory mechanisms have been implicated in HCC pathophysiology. Surgical resection and liver transplants are currently used to treat HCC. Consequently, there exists a decisive requirement to explore possible alternative chemopreventive and therapeutic strategies for HCC. The use of dietary antioxidants and micronutrients has been proposed as a useful means for the HCC management. Trace elements such as selenium are involved in several major metabolic pathways as well as antioxidant defense systems. In particular, selenium is an important oligo-element that plays a central role in cellular redox processes even if the amount necessary for the cell functions is in a very narrow range. However, selenium is involved in the prevention of numerous chronic diseases and cancers. This review will examine the potential role of selenium in HCC prevention and treatment and, in detail, focus on: i) description of selenium in biological systems and in mammalian proteins, ii) involvement of selenium in HCC, iii) in vivo and in vitro effects of selenium in preclinical models of HCC and iv) potential challenges involved in the selenium use in the prevention and treatment of HCC.Mini Reviews in Medicinal Chemistry 05/2011; 11(7):599-610. DOI:10.2174/138955711795906950 · 3.19 Impact Factor