A conformational transition state accompanies tryptophan activation by B. stearothermophilus tryptophanyl-tRNA synthetase

B. stearothermophilus tryptophanyl-tRNA synthetase catalysis proceeds via high-energy protein conformations. Unliganded MD trajectories of the pretransition-state complex with Mg(2+)ATP and the (post) transition-state analog complex with adenosine tetraphosphate relax rapidly in opposite directions, the former regressing, the latter progressing along the structural reaction coordinate. The two crystal structures (rmsd 0.7 A) therefore lie on opposite sides of a conformational free-energy maximum as the chemical transition state forms. SNAPP analysis illustrates the complexity of the associated long-range conformational coupling. Switching interactions in four nonpolar core regions are locally isoenergetic throughout the transition. Different configurations, however, propagate their effects to unfavorable, longer-range interactions at the molecular surface. Designed mutation shows that switching interactions enhance the rate, perhaps by destabilizing the ground state immediately before the transition state and limiting nonproductive diffusion before and after the chemical transition state, thereby reducing the activation entropy. This paradigm may apply broadly to energy-transducing enzymes.     

Nonglutamate pore residues in ion selection and conduction in voltage-gated Ca(2+) channels

High-affinity, intrapore binding of Ca(2+) over competing ions is the essential feature in the ion selectivity mechanism of voltage-gated Ca(2+) channels. At the same time, several million Ca(2+) ions can travel each second through the pore of a single open Ca(2+) channel. How such high Ca(2+) flux is achieved in the face of tight Ca(2+) binding is a current area of inquiry, particularly from a structural point of view. The ion selectivity locus comprises four glutamate residues within the channel's pore. These glutamates make unequal contributions to Ca(2+) binding, underscoring a role for neighboring residues in pore function. By comparing two Ca(2+) channels (the L-type alpha(1C), and the non-L-type alpha(1A)) that differ in their pore properties but only differ at a single amino acid position near the selectivity locus, we have identified the amino-terminal neighbor of the glutamate residue in motif III as a determinant of pore function. This position is more important in the function of alpha(1C) channels than in alpha(1A) channels. For a systematic series of mutations at this pore position in alpha(1C), both unitary Ba(2+) conductance and Cd(2+) block of Ba(2+) current varied with residue volume. Pore mutations designed to make alpha(1C) more like alpha(1A) and vice versa revealed that relative selectivity for Ba(2+) over K(+) depended almost solely on pore sequence and not channel type. Analysis of thermodynamic mutant cycles indicates that the motif III neighbor normally interacts in a cooperative fashion with the locus, molding the functional behavior of the pore.     

Characteristics of multiple resistance in methicillin resistant strains of staphylococci in patients with otorhinolaryngologic diseases]

Antibiotic resistance of 155 methicillin resistant strains of staphylococci of various species was investigated. The strains were susceptible to macrolides, gentamicin and rifampicin. The antibiotics could be recommended for the treatment of otorhinolaryngologic diseases.     

Experimental study of Microcystis-associated and free-living cyanobacteria

In the experiment with water from the hypereutrophic Lake Frederiksborg Slotso (Denmark) sampled during the autumn peak of Microcystis growth, the quantity and production of free-living and cyanobacteria-associated heterotrophic bacteria were determined, as well as the extracellular enzymatic (aminopeptidase) activity. The functional diversities of associated and free-living bacterial communities were additionally compared using BIOLOG GN microplates to reveal the possible export of Microcystis-attached bacteria into ambient water. It has been shown that the cell size, production values, and growth rates of associated bacteria were less than those of free-living bacteria. At the same time, the potential aminopeptidase activity of associated bacteria was always higher than that of free-living bacteria. The experimental results have shown significant compositional differences in the structure of bacterial communities from different habitats.     

Polyhydroxylated steroid compounds from the Far Eastern starfish Distolasterias nipon

Two new steroid glycosides: distolasteroside D6, (24S)-24-O-(beta-D-xylopyranosyl)-5alpha-cholestane-3beta,6alpha,8,15beta,16beta,24-hexaol, and distolasteroside D7. (22E,24R)-24-O-(beta-D-xylopyranosyl)-5alpha-cholest-22-ene-3beta,6alpha,8,15beta,24-pentaol were isolated along with the previously known distolasterosides D1, D2, and D3, echinasteroside C, and (25S)-5alpha-cholestane-3beta,4beta,6alpha,7alpha,8,15alpha,16beta,26-octaol from the Far Eastern starfish Distolasterias nipon. The structures of new compounds were elucidated by NMR spectroscopy and MALDI TOF mass spectrometry. Like neurotrophins, distolasterosides D1, D2, and D3 were shown to induce neuroblast differentiation in a mouse neuroblastoma C 1300 cell culture.     

Immunity features in patients with upper respiratory tract disease caused by Chlamydia

Comparative analysis of results of clinical and laboratory evaluation of patients with chronic nasal or nasal sinuses' diseases (chronic rhinitis or maxillary sinusitis) associated or not associated with Chlamydia infection was performed. It was shown that in patients infected with Chlamydia, along with unidirectional changes typical for all patients irrespective from presence or absence of Chlamydia, the features of immune response against these infectious agents take place.     

Elucidation of structure of lipid A from the marine Gram-negative bacterium Pseudoalteromonas haloplanktis ATCC 14393T

The chemical structure of lipid A from the marine gamma-proteobacterium Pseudoalteromonas haloplanktis ATCC 14393T, a main product of lipopolysaccharide hydrolysis (1% AcOH), was determined using chemical methods and NMR spectroscopy. The lipid A was shown to be beta-1,6-glucosaminobiose 1,4'-diphosphate acylated with two (R)-3-hydroxyalkanoic acid residues at C3 and C3' and amidated with one (R)-3-hydroxydodecanoyl and one (R)-3-dodecanoyloxydodecanoyl residue at N2 and N2', respectively.