Project description: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.
Project description:The mechanisms for regulation of ribosomal gene expression have been characterized in eukaryotes and eubacteria, but not yet in archaebacteria. We have studied the regulation of the synthesis of ribosomal proteins MvaL1, MvaL10, and MvaL12, encoded by the MvaL1 operon of Methanococcus vannielii, a methanogenic archaebacterium. MvaL1, the homolog of the regulatory protein L1 encoded by the L11 operon of Escherichia coli, was shown to be an autoregulator of the MvaL1 operon. As in E. coli, regulation takes place at the level of translation. The target site for repression by MvaL1 was localized by site-directed mutagenesis to a region within the coding sequence of the MvaL1 gene commencing about 30 bases downstream of the ATG initiation codon. The MvaL1 binding site on the mRNA exhibits similarity in both primary sequence and secondary structure to the L1 regulatory target site of E. coli and to the putative binding site for MvaL1 on the 23S rRNA. In contrast to other regulatory systems, the putative MvaL1 binding site is located in a sequence of the mRNA which is not in direct contact with the ribosome as part of the initiation complex. Furthermore, the untranslated leader sequence is not involved in the regulation. Therefore, we suggest that a novel mechanism of translational feedback regulation exists in M. vannielii.
Project description:Methanococcus maripaludis is a methanogenic Archaea that conserves energy from molecular hydrogen to reduce carbon dioxide to methane. Chemostat grown cultures limited for hydrogen, phosphate, or leucine were compared to determine the regulatory response to hydrogen limitation. This was done by comparing hydrogen limited cultures to both leucine limited and phosphate limited cultures. Slow and rapid growing samples limited for either hydrogen or phosphate were compared to determine the regulatory effects of growth rate. Keywords: archaea, hydrogen, leucine, phosphate, nutrient limitation, growth rate, methanogen