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The two-component BvrS/BvrR system is essential for Brucella abortus virulence. It was shown previously that its dysfunction abrogates expression of some major outer membrane proteins and increases bactericidal peptide sensitivity. Here, we report that BvrS/BvrR mutants have increased surface hydrophobicity and susceptibility to killing by nonimmune serum. The bvrS and bvrR mutant lipopolysaccharides (LPSs) bound more polymyxin B, chimeras constructed with bvrS mutant cells and parental LPS showed augmented polymyxin B resistance, and, conversely, parental cells and bvrS mutant LPS chimeras were more sensitive and displayed polymyxin B-characteristic outer membrane lesions, implicating LPS as being responsible for the phenotype of the BvrS/BvrR mutants. No qualitative or quantitative changes were detected in other envelope and outer membrane components examined: periplasmic [beta](1-2) glucans, native hapten polysaccharide, and phospholipids. The LPS of the mutants was similar to parental LPS in O-polysaccharide polymerization and fine structure but showed both increased underacylated lipid A species and higher acyl-chain fluidity that correlated with polymyxin B binding. These lipid A changes did not alter LPS cytokine induction, showing that in contrast to other gram-negative pathogens, recognition by innate immune receptors is not decreased by these changes in LPS structure. Transcription of Brucella genes required for incorporating long acyl chains into lipid A (acpXL and lpxXL) or implicated in lipid A acylation control (bacA) was not affected. We propose that in Brucella the outer membrane homeostasis depends on the functioning of BvrS/BvrR. Accordingly, disruption of BvrS/BvrR damages the outer membrane, thus contributing to the severe attenuation manifested by bvrS and bvrR mutants.

Issues concerning the examination of X-ray diffraction data of the stepwise melting process of trimyristin nanoparticles are discussed.

Experiments were conducted to investigate the effects of oxygen on the cerium-catalyzed Belousov-Zhabotinsky reaction at low catalyst concentrations. Results suggested that the decrease in average Ce4+ concentration in the presence of oxygen is a property of the MA/Ce4+ system involving malonyl radicals. Moreover, the effect of oxygen on the mechanism of oxidation of malonic acid by Ce4+ in acidic medium is significantly affected by the presence of bromate.

Research was conducted to examine a ligand-binding protein (SIS2) of a glutamate receptor ion channel (GluR) via solution scattering studies to investigate GluR-binding and signal-transduction mechanisms. The solution scattering properties of the free and agonist-bound states of a ligand-binding domain of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptor subunit GluRD were compared. Results indicate a molecular envelope for the construct in solution.

Research was conducted to examine the properties of a mutant hexokinase I, in which residues critical to the stability of the dimer have been changed by directed mutation. The resulting mutant was shown to exist in solution as a monomer at elevated concentrations of enzyme, either in the presence or absence of ligands. Results indicate that the allosteric regulation of catalysis in monomeric hexokinase I probably involves an interface between the N- and C-terminal halves, similar to ones defined by crystal structures.

The quaternary structure of the V1 ATPase from the tobacco hornworm Manduca sexta and the F1 ATPase from Escherichia coli was characterized using small-angle X-ray scattering. The radii of gyration of the V1 and F1 complexes as well as the shape of the V1 ATPase were also determined. Experimental results showed that a seventh mass, which is thought to be the stalk that links V1 with the membrane domain V0 in the intact V1V0-ATPase, extends perpendicularly to the center of the hexameric unit.

A study was conducted to analyze the quarternary structures of the thiamine diphosphate dependent enzyme pyruvate decarboxylase from Saccharomyces cerevisiae, Zymomonas mobilis and Pisum sativuum. X-ray solution scattering was carried out to perform the analysis while solutions were prepared from enzyme stock solutions. Results indicated that mutant E51 is a critical component in cofactor binding and catalytic activity.

Magnesium ions initiate the formation of the catalytically active dimer and the activity of enzyme I from the phosphoenolpyruvate system of Staphylococcus carnosus. X-ray scattering patterns of the enzyme reveals an increase in the radius of gyration and the molecular mass in the presence of Mg2+ and the substrate, phosphoenolpyruvate. The substrate appears to shift the equilibrium towards the formation of the active dimer by reducing the rate of dissociation of the phophorylated dimer.

Data analysis methods to simultaneously evaluate X-ray and neutron scattering data yield a model of the native Escherichia coli 50S subunit shape in solution and of the core that is enriched in RNA. Comparison of this model with three electron microscopic models reveals that the 50S subunit shape agrees well with the electron microscopic models of isolated particles. The model achieved from ordered sheets agrees with the RNA-rich core, indicating its favorable bias toward the RNA.

The pH dependence of the three-dimensional quarternary structure of yeast pyruvate decarboxylase (PDC) was examined in the pH range from 6.2 to 8.4 by a synchroton radiation solution x-ray scattering study. The equilibrium between tetramers and dimers occurs at about pH 7.5 and the PDC's catalytic activity is dependent on the volume fraction of tetramer. The experimental observations of an equilibrium shift and formation of octamers were further analyzed. These observations were found to indicate that the dimers must undergo a conformational change when forming the tetramer, as suggested by earlier studies.

Ultrafast (ps) time-resolved X-ray scattering is used for analyzing the structural dynamics of [Ru.sub.3][(CO).sub.12] in cyclohexane after photolysis. The difference radial distribution functions (RDFs) have shown the depletion of Ru-Ru bonds in the initial [Ru.sub.3][(CO).sub.12] molecule and formation of [Ru.sub.3][(CO).sub.10] as the major photoproduct.