The hybrid cluster proteins from the sulfate reducing bacteria Desulfovibrio desulfuricans ATCC 27774 ( Dd) and Desulfovibrio vulgaris strain Hildenborough ( Dv) have been isolated and crystallized anaerobically. In each case, the protein has been reduced with dithionite and the crystal structure of the reduced form elucidated using X-ray synchrotron radiation techniques at 1.25 A and 1.55 A resolution for Dd and Dv, respectively. Although the overall structures of the proteins are unchanged upon reduction, there are significant changes at the hybrid cluster centres. These include significant movements in the position of the iron atom linked to the persulfide moiety in the oxidized as-isolated proteins and the sulfur atom of the persulfide itself. The nature of these changes is described and the implications with respect to the function of hybrid cluster proteins are discussed.

The Desulfovibrio gigas aldehyde oxidoreductase contains molybdenum bound to a pterin cofactor and [2Fe-2S] centers. The enzyme was characterized by SDSPAGE, gel-filtration and analytical ultracentrifugation experiments. It was crystallized at !"C, pH 7.2, using isopropanol and MgC1, as precipitants. The crystals diffract beyond 0.3-nm (3.0-A) resolution and belong to space group P6,22 or its enantiomorph, with cell dimensions u = b = 14.45 nm and c = 16.32 nm. There is one subunit/asymmetric unit which gives a packing density of 2.5 X nm'/Da (2.5 A3/Da), consistent with the experimental crystal density, p = 1.14 g/cm3. One dimer (approximately 2 X 100 kDa) is located on a crystallographic twofold axis.The detailed knowledge of the structure and the catalytic mechanism of molybdenum-containing enzymes has considerably increased during the last decade [I -61 and, in particular, the biochemistry of aldehyde oxidoreductases has been extensively studied [4, 51. Molybdenum is a relevant transition metal in biological systems. Two groups of molybdo-proteins have been described. In the first group Mo is associated with iron in a complex cluster type structure (FeMocofactor) in the nitrogenase enzyme. Recently, a structural model of the FeMoco was proposed based on crystallographic analysis, consisting of [4Fe,3S] and [lMo,3Fe,3S] clusters bridged by three nonprotein ligands [7, 81. In the second group Mo is contained in an organic structural component (pterin), designated as Mocofactor (molybdopterin), generally associated with ironsulfur centers and/or a flavin or heme center, as in the case of molybdenum oxotransferases [6].From sulfate-reducing bacteria (strict anaerobes) enzymes related to the second group have been isolated and characterized [9-171. They represent unique situations for the presence of such a group of enzymes in the prokaryotic world, since most often these proteins are studied in eukaryotes (e.g. plants, insects and higher animals).The molybdenum iron-sulfur protein (MOP) isolated from D. gigas has analogies with the molybdenum hydrox- An important advance on these studies was the possibility to isolate the enzyme from 57Fe-enriched media with obvious interest for an iron-sulfur-center site labelling, enhanced sensitivity of the Mossbauer studies (an advantage with respect to mammalian systems) and the possibility of a direct measurement of substrate binding [14]. Previously described molybdenum (V) resting-type and slow-type EPR signals and the extended-X-ray-absorption fine-structure (EXAFS) spectrum of the molybdenum center indicated close similarities to desulfo-xanthine oxidase (inactive) [lo-121. In addition, it was later demonstrated for MOP, a new Mo(V) EPR signal (rapid type 2) centered at EPR average g-value (gav) of 1.9742, similar to those observed for xanthine and aldehyde oxidases [12]. These rapid EPR signals have been shown, in these proteins, to be physiologically significant, as they develop within the enzymeturnover time scale. A molybdenum cofactor, liberated from the protei...

Crystals of the fully oxidized form of desulfoferrodoxin were obtained by vapor diffusion from a solution containing 20% PEG 4000, 0.1 M HEPES buffer, pH 7.5, and 0.2 M CaCl2. Trigonal and/or rectangular prisms could be obtained, depending on the temperature used for the crystal growth. Trigonal prisms belong to the rhombohedral space group R32, with a = 112.5 A and c = 63.2 A; rectangular prisms belong to the monoclinic space group C2, with a = 77.7 A, b = 80.9 A, c = 53.9 A, and beta = 98.1 degrees. The crystallographic asymmetric unit of the rhombohedral crystal form contains one molecule. There are two molecules in the asymmetric unit of the monoclinic form, in agreement with the self-rotation function.

Nine heme cytochrome c (9Hcc) is a monomeric multi‐heme cytochrome c found in the sulfate‐reducing bacteria of Desulfovibrio desulfuricans (Dd) ATCC 27774 and Desulfovibrio desulfuricans Essex 6. The polypeptide chain comprises 296 residues and wraps around nine hemes of type‐c that bind the polypeptide chain through thioether bridges to cysteine residues. This represents the first known structure of a multi‐heme cytochrome where copies of a tetra‐heme cytochrome c 3 ‐like fold are present in the same polypeptide chain. The high homology between 9Hcc and the C‐terminal region of Desulfovibrio vulgaris Hildenborough (DvH) Hmc, as well as the presence of the 9Hcc gene within an operon similar to that of the DvH Hmc, strongly support the proposal that 9Hcc is the high‐molecular‐weight cytochrome of Dd. Several in vitro studies, as well as our crystallographic and modeling studies suggest that cytochrome c 3 is the mediator between the [NiFe] hydrogenase and 9Hcc in Dd.

Tetraheme cytochromes c 3 constitute the best‐studied group among the multiheme cytochromes belonging to the class III of Ambler's classification. Since 1954, when cytochrome c 3 was isolated from Desulfovibrio vulgaris for the first time by Postgate, these proteins have been widely characterized, especially those from the Desulfovibrio ( D .) genus. All these cytochromes have their heme group attached to the polypeptide chain by cysteine residues and show bis‐histidinyl coordination of the heme iron and a highly conserved heme‐binding motif (CXXCH or CXXXXCH). Cytochromes c 3 show a wide variety of redox potentials, ranging from 0 to −400 mV, are usually periplasmatic proteins, and are believed to play key roles in the electron transfer chains. Recently, the cytochrome c 3 group was divided into two main types on the basis of structural, functional, and genetic differences: type I cytochrome c 3 (TpI‐ c 3 ) and type II cytochrome c 3 (TpII‐ c 3 ). This paper reviews their structural, spectroscopic, and functional properties, based on the wealth of information currently available. These include physicochemical properties, redox mechanisms, coupling between electron and proton transfer, and data concerning the interaction with their redox partners obtained by experimental and molecular modeling methods.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

No abstract