Jorge Lampreia

Adenylate kinase (AK) mediates the reversible transfer of phosphate groups between the adenylate nucleotides and contributes to the maintenance of their constant cellular level, necessary for energy metabolism and nucleic acid synthesis. The AK were purified from crude extracts of two sulfate-reducing bacteria (SRB), Desulfovibrio (D.) gigas NCIB 9332 and Desulfovibrio desulfuricans ATCC 27774, and biochemically and spectroscopically characterised in the native and fully cobalt- or zinc-substituted forms. These are the first reported adenylate kinases that bind either zinc or cobalt and are related to the subgroup of metal-containing AK found, in most cases, in Gram-positive bacteria. The electronic absorption spectrum is consistent with tetrahedral coordinated cobalt, predominantly via sulfur ligands, and is supported by EPR. The involvement of three cysteines in cobalt or zinc coordination was confirmed by chemical methods. Extended X-ray absorption fine structure (EXAFS) indicate that cobalt or zinc are bound by three cysteine residues and one histidine in the metal-binding site of the ``LID{''} domain. The sequence (129)Cys-X(5)-His-X(15)-Cys-X(2)-Cys of the AK from D. gigas is involved in metal coordination and represents a new type of binding motif that differs from other known zinc-binding sites of AK. Cobalt and zinc play a structural role in stabilizing the LID domain. (C) 2008 Elsevier Inc. All rights reserved.

{Nitrite reductase from the sulfate-reducing bacterium Desulfovibrio desulfuricans ATCC 27774 is a multihaem (type c) membrane-bound enzyme that catalyzes the dissimilatory conversion of nitrite to ammonia. Crystals of the oxidized form of this enzyme were obtained using PEG and CaCl2 as precipitants in the presence of 3-(decylmethylammonium)propane-1-sulfonate and belong to the space group P2(1)2(1)2(1), With unit-cell parameters a = 78.94

The primary structure of desulfoferrodoxin from Desulfovibrio desulfuricans ATCC 27774, a redox protein with two mononuclear iron sites, was determined by automatic Edman degradation and mass spectrometry of the composing peptides, It contains 125 amino acid residues of which five are cysteines, The first four, Cys-9, Cys-12, Cys-28 and Cys-29, are responsible for the binding of Center I which has a distorted tetrahedral sulfur coordination similar to that found in desulforedoxin from D. gigas, The remaining Cys-115 is proposed to be involved in the coordination of Center II, which is probably octahedrally coordinated with predominantly nitrogen/oxygen containing ligands as previously suggested by Mossbauer and Raman spectroscopy.