a classical heme-binding motif for periplasmic proteins. The catalytic heme binds a ... these enzymes are membrane-bound and very similar to the ubiquitous ...
Biochemical Society Transactions (2002) Volume 30, Part 3
A16 Cobalamin (Vitamin B12 ) Biosynthesis in Rhodobacter
A18 Structure and function of the nickel
capsulatus. H.M. McGoldrick Queen Mary, University of London, E l 4NS.
methanogenic archaea
Please refer t o abstract number 12. This abstract was originally submitted as a poster, and o n the basis of its scientific interest and merit, was chosen by the colloquium organizers to be presented as an oral communication, as well as a poster.
A17 Bacterial cytochrome c nitrite reductase: three-dimensional structure and spectroscopy of the multiheme enzyme
P.M.H. Kroneck Farhbereich Biologie, Universitaet Konstanz, 78417 Konstanz, Germany Cytochrome c nitrite reductase (NiR) is part of the anaerobic energy metabolism of dissimilatory nitrate reduction to ammonia in bacteria, and can also use NO and sulfite as substrates. The protein is a homodimer, the monomer has a molecular mass of 58614, with 492 amino acid residues and five heme groups. The heme groups are in close contact and have Fe-Fe distances between 9 and 12.8 A. They are arranged as a group of three almost coplanar with the heme situated at the right margin forming the active site in this monomer. The other two hemes in each monomer are further apart and are not coplanar with the heme triple group. All hemes except the active site heme are bis-histidinyl-coordinatedand are linked to the peptide backbone via thioether bonds to the cysteine residues of a classical heme-binding motif for periplasmic proteins. The catalytic heme binds a lysine in the 5th place as a novel structural motif. The unusual EPR and structural properties of NiR and NiR mutant proteins will be discussed and compared t o the properties of related multiheme proteins and enzymes.
A5 I
tetrapyrrole F430 in
Rudolf K. Thauer Max Planck Institute for Terrestrial Microbiology, Karl-von-FrischStrasse, 0-35043 Marburg, Germany F430 is a nickel tetrapyrrole found in all archaea that generate methane as endproduct of their energy metabolism and the cofactor is only found in these anaerobic microorganisms in which it functions as the prosthetic group of methyl coenzyme M reductase, the enzyme catalyzing the methane forming step proper (l).The crystal structure of methyl coenzyme M reductase has been resolved to 1.16 A (2,3) and the Ni EPR spectroscopic properties of the enzyme have been characterized in detail (4,5). Based o n quantum chemical studies a catalytic mechanism for methyl coenzyme M reductase has recently been proposed involving a Ni(1) mediated homolytic cleavage of the S-CH3 bond in methyl coenzyme M (6,7). (1) Thauer, R. K. (1998) Microbiology 144:2377-2406. (2) Ermler, U. et al. (1997) Science 278:1457-1462. (3) Grabarse, W. et al. (2001) J. Mol. Biol. 309: 315-330. (4) Mahlert, F. et al. (2002) J. Biol. Inorg. Chem. 7: 101-112. (5) Mahlert, F. et al. (2002) J. Biol. Inorg. Chem.: in press. (6) Pelmenschikov, V. et al. (2001) J. Am. Chem. SOC.:in press. (7) Ghosh, A.. et al. (2001) Curr. Opinion in Chem. Biol. 5: 744-750.
A19 A universal mechanism for fumarate reduction Graeme A. Reid, Christopher G. Mowat, Caroline S. Miles, Kate Pankhurst, Malcolm D. Walkinshaw and Stephen K. Chapman Institute of Cell and Molecular Biology, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JR Fumarate reductases enable bacteria to respire anaerobically with fumarate as a terminal electron acceptor. In most known bacteria these enzymes are membrane-bound and very similar t o the ubiquitous succinate dehydrogenase. Shewanella species produce a soluble, periplasmic fumarate reductase that depends o n electron input from membrane-bound quinols via a c-type cytochrome whereas the membrane-bound enzymes utilise a series of iron-sulfur centres. In contrast to these differences in the reduction of the enzyme, the active sites for fumarate reduction are very well conserved in FAD-containing polypeptides. We have probed the reaction mechanism in the fumarate reductase from Shewanella frigidimarina by a combination of site-directed mutagenesis, kinetics, spectroscopy and crystallography. We have shown the importance of Arg544, His504 and His365 in substrate binding. Fumarate is reduced by hydride transfer from FAD and formation of the product succinate is facilitated by proton transfer from Arg402. A proton-conducting channel involving Arg381 and Glu378 allow reprotonation of this catalytic arginine residue. Comparison with other fumarate reductase structures indicates that this reaction mechanism is conserved throughout this enzyme family.
0 2002 Biochemical Society
