RESUMO
Thermostable enzymes employ various structural features dictated at the amino-acid sequence level that allow them to maintain their integrity at higher temperatures. Many hypotheses as to the nature of thermal stability have been proposed, including optimized core hydrophobicity and an increase in charged surface residues to enhance polar solvent interactions for solubility. Here, the three-dimensional structure of the family GH11 xylanase from the moderate thermophile Thermobifida fusca in its trapped covalent glycosyl-enzyme intermediate complex is presented. Interactions with the bound ligand show fewer direct hydrogen bonds from ligand to protein than observed in previous complexes from other species and imply that binding of the xylan substrate involves several water-mediated hydrogen bonds.
Assuntos
Actinomycetales/enzimologia , Endo-1,4-beta-Xilanases/química , Cristalografia por Raios X , Ligação de Hidrogênio , Modelos Moleculares , Estrutura Terciária de ProteínaRESUMO
Global gene expression patterns of Bacillus subtilis in response to subinhibitory concentrations of protein synthesis inhibitors (chloramphenicol, erythromycin, and gentamicin) were studied by DNA microarray analysis. B. subtilis cultures were treated with subinhibitory concentrations of protein synthesis inhibitors for 5, 15, 30, and 60 min, and transcriptional patterns were measured throughout the time course. Three major classes of genes were affected by the protein synthesis inhibitors: genes encoding transport/binding proteins, genes involved in protein synthesis, and genes involved in the metabolism of carbohydrates and related molecules. Similar expression patterns for a few classes of genes were observed due to treatment with chloramphenicol (0.4x MIC) or erythromycin (0.5x MIC), whereas expression patterns of gentamicin-treated cells were distinct. Expression of genes involved in metabolism of amino acids was altered by treatment with chloramphenicol and erythromycin but not by treatment with gentamicin. Heat shock genes were induced by gentamicin but repressed by chloramphenicol. Other genes induced by the protein synthesis inhibitors included the yheIH operon encoding ABC transporter-like proteins, with similarity to multidrug efflux proteins, and the ysbAB operon encoding homologs of LrgAB that function to inhibit cell wall cleavage (murein hydrolase activity) and convey penicillin tolerance in Staphylococcus aureus.