SUMMARYMaturation of iron-sulfur proteins is achieved by the SUF machinery in a wide number of Eubacteria and Archaea as well as eukaryotic chloroplasts. This machinery is encoded in E. coli by the sufABCDSE operon, where three Suf components, SufB, SufC, and SufD, form a complex and appear to provide an intermediary site for the iron-sulfur cluster assembly. Here we report the quaternary structure of SufC 2 -SufD 2 complex in which SufC is bound to the C-terminal domain of SufD.Comparison with the monomeric structure of SufC revealed conformational change of the active site residues: SufC becomes competent for ATP-binding and hydrolysis upon association with SufD. The two SufC subunits were spatially separated in the SufC 2 -SufD 2 complex, whereas cross-linking experiments in solution have indicated that two SufC molecules associate with each other in the presence of Mg 2+ and ATP. Such dimer formation of SufC may lead to a gross structural change of the SufC 2 -SufD 2 complex. Furthermore, genetic analysis of SufD revealed an essential histidine residue buried inside the dimer interface, suggesting that conformational change may expose this crucial residue. These findings together with biochemical characterization of the SufB-SufC-SufD complex have led us to propose a model for the iron-sulfur cluster biosynthesis in the complex.

SPF Sprague-Dawley rats and ICR mice were inoculated with either Streptococcus mutans MT8148R (serotype c) or 6715 (g), and the influence of inoculum size, inoculum frequency, and sucrose on the establishment of S. mutans in the oral cavity was examined. Successful colonization of S. mutans in the experimental animals was absolutely dependent on the number of the cells introduced orally. Furthermore, inoculum frequency and sucrose seemed to act as secondary factors to modify the establishment of S. mutans, and it is suggested that high inoculum frequency may decrease the inoculum size necessary for the colonization of S. mutans in the oral cavity.

Thirty-four female rats (18 days old) were infected with Streptococcus mutans MT8148R (serotype c) or 6715 (g). Diets containing different proportions of sucrose were used to prepare the dams which harbored various levels of S.mutans in their oral cavity. Around 66 days of age, the female rats were bred and 34 dams subsequently bore 322 offspring. The dams were killed upon weaning (20 days of age) of their respective litters. There were positive correlations between the recovery of inoculated S. mutans and the caries incidence in the dams. Transmission of S. mutans from a dam to her offspring was studied in 10-, 15-, 20-, 27-, 34-, 41-, 48-, and 55-day-old rats by evaluating the recover of S. mutans from the offspring. Positive correlation between the magnitudes of recovered S. mutans MT8148R from dams and their offspring was found in all ages of young rats examined. Furthermore, caries incidence in young rats was found to be positively correlated with the recovery of both strains of S. mutans as well as with incidence of caries in their respective dams.

A bacteriocin from serotype c Streptococcus mutans strain C3603 was examined for its inhibitory effect on experimental dental caries in rats infected with S. mutans MT8148R (serotype c). Significant reduction in the incidence of dental caries was found only when bacteriocin was incorporated both in the drinking water and in the diet at a high concentration.However, caries reduction was not as great as expected and the addition of bacteriocin to drinking water alone had no effect on the recovery of S. mutans, plaque deposition or caries incidence. The bacteriocin activity must have been reduced in the oral cavity of rats, and the reasons were examined.Bacteriocin-resistant mutants were not detected and the bacteriocin was not inactivated by saliva.Whereas the bacteriocin did not kill the S. mutans cells grown in a sucrosecontaining medium, it completely killed the cells grown in a sucrose-free medium.

IsdG and IsdI are paralogous proteins from Staphylococcus aureus that reductively degrade hemin. Final heme degradation products of IsdG and IsdI are yet to be elucidated, nor has it been determined how oxygen binds to initiate the reaction. The crystal structures of an inactive N7A variant of IsdG in complex with Fe 3+ -protoporphyrin IX (IsdG-hemin) and of IsdI in complex with cobalt protoporphyrin IX (IsdI-CoPPIX) were solved to 1.8 Å or better resolution. These structures show that the metalloporphyrins are buried into similar deep clefts and the propionic acids form salt bridges to two Arg residues. His77 (IsdG) or His76 (IsdI), a residue required for activity, is coordinated to Fe 3+ or Co 3+ atoms, respectively. The bound porphyrin rings form extensive steric interactions in the binding cleft such that the porphyrin rings are highly distorted from the planar. This distortion can be described as ruffled and places the b-and d-meso carbons close to the distal oxygen-binding site. In the structure of IsdI-CoPPIX, the distal side of the CoPPIX accommodates a chloride ion in a cavity formed through a conformational change in Ile55. The chloride ion participates in a hydrogen bond to the side chain amide of Asn6. We also have determined the crystal structures of IsdG-hemin and IsdI-hemin bound to cyanide to resolutions of ~1.8 Å. Structural information from these complexes is valuable in understanding the regiospecificity of ring cleavage. We propose a reaction mechanism in which reactive peroxide intermediate proceeds with nucleophilic oxidation at the b-or d-meso carbon of the hemin.Keywords: iron acquisition, heme degradation, staphylococcus aureus P04.03.199 Acta Cryst. (2008). A64, C293Crystal structural analysis of photosystem II with the novel method to reduce X-ray radiation damage Photosystem II (PSII) is a multi-subunit membrane protein complex functioning in photosynthesis. It performs a series of light-induced electron transfer reactions leading to the splitting of water and generation of molecular oxygen. The catalytic center is composed of four manganese atoms and one calcium atom. The detailed locations of these metal atoms are not fully understood. Recent X-ray absorption fine structure analysis has shown that the Mn4Ca-cluster is seriously damaged by X-ray irradiation onto PSII crystals resulting in changes in the coordination structure among these metal atoms. In order to reveal the intact structure of the Mn4Ca-cluster, we adopted a slide-oscillation method to collect the low-dose X-ray data for the crystal structure analysis. In this method, the irradiation point was slid to an adjacent point on the crystal along the oscillation axis after recording of every image and after some slides the irradiation point was brought back to the initial position. These slides were repeated through the required oscillation range. This method reduced the overlap of the irradiated regions in each cross section of the crystal 20 times lower than the normal oscillation method. Using X-ray beam (0.035 x 0.035 mm...