Proteolytic degradation of staphylococcal alpha-toxin

Free-Energy-Based Gene Mutation Detection Using LNA Probes

We have developed a label-free approach for direct detection of gene mutations using free-energy values that are derived from single-molecule force spectroscopy (SMFS)-based nucleic acid unbinding experiments. From the duplex unbinding force values acquired by SMFS, the force-loading-rate-independent Gibbs free-energy values were derived using Jarzinsky's equality treatment. Because it provides molecule-by-molecule information, this approach is a major shift compared to the earlier reports on label-free detection of DNA sequences, which are mostly based on ensemble level data. We tested our approach in the disease model framework of multiple drug-resistant tuberculosis using the nuclease-resistant and conformationally rigid locked nucleic acid probes that are a robust and efficient alternative to the DNA probes. All of the major mutations in Mycobacterium tuberculosis (MTB), as relevant to MTB's resistance to the first-line anti-TB drugs rifampicin and isoniazid, could be identified, and the wild type could be discriminated from the most prevalent mutation and the most prevalent mutation from the less occurring ones. Our approach could also identify DNA sequences (45 mer), having overhang stretches at different positions with respect to the complementary stretch. Probably for the first time, the findings show that free-energy-based detection of gene mutations is possible at molecular resolution.

Effect of phenethyl alcohol on Staphylococcus aureus alpha-lysin production

Phenethyl alcohol, at the maximum concentration which did not inhibit growth (0.3% [vol/vol]), inhibited the production of alpha-lysin and exoproteases but not that of delta-lysin in Staphylococcus aureus Wood 46. The inhibition of alpha-lysin was reversible, and transient accumulation of cell-associated alpha-lysin occurred in the presence of PEA. A precursor of alpha-lysin ca. 3,000 daltons larger than extracellular alpha-lysin was immunologically detected in the sodium dodecyl sulfate extracts of membranes and whole cells of phenethyl alcohol-treated S. aureus cultures. Also, a degraded form of alpha-lysin was detected in membranes prepared from cells lysed by lysostaphin but not in membranes from cells lysed with an X-press.