Respiratory enzymes from Shewanella MR-1

• Main Author: Atanasiu, Doina
• Published: University of Edinburgh 2001
• Subjects: 579
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.641135

<i>Shewanella </i>MR-1 is a Gram-negative, facultatively anaerobic bacterium isolated from Lake Oneida, New York. It can couple its anaerobic growth to the reduction of a wide variety of compounds such as nitrate, nitrite, TMAO, DMSO, fumarate, manganese(IV) and iron(III) oxides, sulfite and thiosulfate. Analysis of the genome sequence reveals the presence of a large number of respiratory enzymes. Three of these proteins were selected for further study: a decaheme cytochrome <i>c</i>, a heptaheme cytpchrome <i>c </i>and a flavoprotein. Decaheme 129 (Cyc129) is 37% similar to MtrC, a decaheme protein from the same organisms that have been shown to be involved in iron(III) and manganese(IV) respiration. The DNA sequence indicated the presence of a lipoprotein signal sequence but the protein is loosely associated to the membrane. Compared to the wild-type strain, no phenotypic differences were noted when the <i>cyc129 </i>gene was disrupted by the insertion of an antibiotic cassette. The second protein, heptaheme 202 (Cyc202) is a soluble, periplasmic protein and is the only heptaheme cytochrome <i>c </i>in <i>Shewanella </i>MR-1. Phenotypic studies indicate that it might be involved in the electron transport to the outer-membrane located iron-manganese reductases. FccA56 is similar to the flavin domain of flavocytochrome <i>c₃</i>, the fumarate reductase from <i>Shewanella</i> MR-1. The gene encoding this protein is part of a cluster that also encodes a tetraheme <i>c</i>-type cytochrome and a histidine ammonia lyase-like protein. Substitution of the highly conserved amino acids involved in substrate binding suggests that fumarate is not the physiological substrate of FcA56, but has a similar substrate that contains only one carboxylic group. The protein was purified after overexpression in <i>E. coli. </i>A UV-visible absorption spectrum confirmed that the ~52 kDa protein has absorption maxima at 450 and 380 nm, characteristic for flavoproteins.