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Abstract Background Bacteroides fragilis and Bacteroides thetaiotaomicron are members of the normal human intestinal microbiota. However, both organisms are capable of causing opportunistic infections, during which the environmental conditions to which the bacteria are exposed change dramatically. To further explore their potential for contributing to infection, we have characterized the expression in B. thetaiotaomicron of four homologues of the gene encoding the C10 cysteine protease SpeB, a potent extracellular virulence factor produced by Streptococcus pyogenes. Results We identified a paralogous set of genes (btp genes) in the B. thetaiotaomicron genome, that were related to C10 protease genes we recently identified in B. fragilis. Similar to C10 proteases found in B. fragilis, three of the B. thetaiotaomicron homologues were transcriptionally coupled to genes encoding small proteins that are similar in structural architecture to Staphostatins, protease inhibitors associated with Staphopains in Staphylococcus aureus. The expression of genes for these C10 proteases in both B. fragilis and B. thetaiotaomicron was found to be regulated by environmental stimuli, in particular by exposure to oxygen, which may be important for their contribution to the development of opportunistic infections. Conclusions Genes encoding C10 proteases are increasingly identified in operons which also contain genes encoding proteins homologous to protease inhibitors. The Bacteroides C10 protease gene expression levels are responsive to different environmental stimuli suggesting they may have distinct roles in the bacterial-host interaction.

EDTA-derivatized deoxythymidine is presented as a tool for rapid determination of protein binding polarity to DNA by intermolecular paramagnetic relaxation. The method is evaluated and it is found that it has widespread utility in structural and chemical studies of protein-DNA complexes.

Kinetic studies enable the determination of free energies of denaturation for various Staphylococcal nuclease mutants having tyrosine-glutanate hydrogen bonds of different strengths. Fluorine ring substitutions modify the acidity of the tyrosine hydroxyl group and thereby modulates the strength of the hydrogen bond. Each fluorine substitution increases the stabilization energy by an average of 0.56 kcal mol. Linear free energy relation between the pKa of the tyrosine hydroxyl group and free energy change of the mutant proteins indicates the higher stability of intramolecular hydrogen bonds in folded proteins compared to the hydrogen bonds in the unfolded state.

F inegoldia magna is a Gram-positive anaerobic commensal of the human skin microbiota, but also known to act as an opportunistic pathogen. Two primary virulence factors of F . magna are the subtilisin-like extracellular serine protease SufA and the adhesive protein FAF. This study examines the molecular mechanisms F . magna uses when colonizing or establishing an infection in the skin. FAF was found to be essential in the initial adherence of F . magna to human skin biopsies. In the upper layers of the epidermis FAF mediates adhesion through binding to galectin-7 - a keratinocyte cell marker. Once the bacteria moved deeper into the skin to the basement membrane layer, SufA was found to degrade collagen IV which forms the backbone structure of the basement membrane. It also degraded collagen V, whereby F . magna could reach deeper dermal tissue sites. In the dermis, FAF interacts with collagen V and fibrillin, which presumably helps the bacteria to establish infection in this area. The findings of this study paint a clear picture of how F . magna interacts with human skin and explain how it is such a successful opportunistic pathogen in chronic wounds and ulcers. [ABSTRACT FROM AUTHOR]

Analyzes the DNA conformation by P nuclear magnetic resonance (NMR). Spectral dispersion of P signals; Findings on the upfield shifted resonances; Estimation on the lifetime of the complexes from 2D exchange experiments.