Structural and DNA-binding studies on the bovine antimicrobial peptide, indolicidin: evidence for multiple conformations involved in binding to membranes and DNA

Indolicidin, a l3-residue antimicrobial peptide-amide, which is unusually rich in tryptophan and proline, is isolated from the cytoplasmic granules of bovine neutrophils. In this study, the structures of indolicidin in 50% D(3)-trifluoroethanol and in the absence and presence of SDS and D(38)-dodecylphosphocholine were determined using NMR spectroscopy. Multiple conformations were found and were shown to be due to different combinations of contact between the two WPW motifs. Although indolicidin is bactericidal and able to permeabilize bacterial membranes, it does not lead to cell wall lysis, showing that there is more than one mechanism of antimicrobial action. The structure of indolicidin in aqueous solution was a globular and amphipathic conformation, differing from the wedge shape adopted in lipid micelles, and these two structures were predicted to have different functions. Indolicidin, which is known to inhibit DNA synthesis and induce filamentation of bacteria, was shown to bind DNA in gel retardation and fluorescence quenching experiments. Further investigations using surface plasmon resonance confirmed the DNA-binding ability and showed the sequence preference of indolicidin. Based on our biophysical studies and previous results, we present a diagram illustrating the DNA-binding mechanism of the antimicrobial action of indolicidin and explaining the roles of the peptide when interacting with lipid bilayers at different concentrations

Genomic diversity of citrate fermentation in Klebsiella pneumoniae

<p>Abstract</p> <p>Background</p> <p>It has long been recognized that <it>Klebsiella pneumoniae </it>can grow anaerobically on citrate. Genes responsible for citrate fermentation of <it>K. pneumoniae </it>were known to be located in a 13-kb gene cluster on the chromosome. By whole genome comparison of the available <it>K. pneumoniae </it>sequences (MGH 78578, 342, and NTUH-K2044), however, we discovered that the fermentation gene cluster was present in MGH 78578 and 342, but absent in NTUH-K2044. In the present study, the previously unknown genome diversity of citrate fermentation among <it>K. pneumoniae </it>clinical isolates was investigated.</p> <p>Results</p> <p>Using a genomic microarray containing probe sequences from multiple <it>K. pneumoniae </it>strains, we investigated genetic diversity among <it>K. pneumoniae </it>clinical isolates and found that a genomic region containing the citrate fermentation genes was not universally present in all strains. We confirmed by PCR analysis that the gene cluster was detectable in about half of the strains tested. To demonstrate the metabolic function of the genomic region, anaerobic growth of <it>K. pneumoniae </it>in artificial urine medium (AUM) was examined for ten strains with different clinical histories and genomic backgrounds, and the citrate fermentation potential was found correlated with the genomic region. PCR detection of the genomic region yielded high positive rates among a variety of clinical isolates collected from urine, blood, wound infection, and pneumonia. Conserved genetic organizations in the vicinity of the citrate fermentation gene clusters among <it>K. pneumoniae</it>, <it>Salmonella enterica</it>, and <it>Escherichia coli </it>suggest that the13-kb genomic region were not independently acquired.</p> <p>Conclusion</p> <p>Not all, but nearly half of the <it>K. pneumoniae </it>clinical isolates carry the genes responsible for anaerobic growth on citrate. Genomic variation of citrate fermentation genes in <it>K. pneumoniae </it>may contribute to metabolic diversity and adaptation to variable nutrient conditions in different environments.</p

Experiences Using MEMS Accelerometers on Railway Bearers at Switches and Crossings to Obtain Displacement—Awkward Situations

A sleeper, or more generally a “bearer”, moves vertically under a passing train load. The extent of this motion depends on the static and dynamic load of the train, the train speed, and the support conditions at the bearer and its neighbours. Excessive motion, typically from voiding see-sawing, low support stiffness or possibly excessive stiffness, or even too little stiffness, are all of interest to maintainers. Typically, problems arise around transition zones, switches and crossings, but plain track with poor support can also be a problem. Within the last decade, low-cost micro-electro-mechanical system (MEMS) accelerometers have been used to capture the time history of vertical motion for use in condition monitoring. Existing condition monitoring systems often overlook or sometimes even ignore the possibility of problematic data, which seem to be common in monitored locations. It is essential to understand whether such “bad” data require further attention. Three problematic sites are presented, focussing on examples where the acceleration was higher than expected or the computed displacement was not as expected. Potential causes include wheel defects, hammering of the ballast by a hanging bearer, or high acceleration at some structural resonant frequency. The present paper aims to show the challenges of using MEMS accelerometers to collect data for condition monitoring and offers insights into the sort of problematic data that may be collected from real sites