DNA gyrase is a major bacterial protein that is involved in replication and transcription and catalyzes the negative supercoiling of bacterial circular DNA. DNA gyrase is a known target for antibacterial agents since its blocking induces bacterial death. Quinolones, coumarins, and cyclothialidines have been designed to inhibit gyrase. Significant improvements can still be envisioned for a better coumarin-gyrase interaction. In this work, we obtained the crystal costructures of the natural coumarin clorobiocin and a synthetic analogue with the 24 kDa gyrase fragment. We used isothermal titration microcalorimetry and differential scanning calorimetry to obtain the thermodynamic parameters representative of the molecular interactions occurring during the binding process between coumarins and the 24 kDa gyrase fragment. We provide the first experimental evidence that clorobiocin binds gyrase with a stronger affinity than novobiocin. We also demonstrate the crucial role of both the hydroxybenzoate isopentenyl moiety and the 5'-alkyl group on the noviose of the coumarins in the binding affinity for gyrase.

There is strong evidence that the amyloid-β peptide (Aβ) plays a crucial role in the pathogenesis of Alzheimer's disease (AD), a lethal neurodegenerative disorder of the elderly. During pathology development, the peptide as well as its various chemically modified isoforms is accumulated in specific brain tissues as characteristic proteinaceous deposits, the so-called amyloid plaques, which are the pathomorphological mark of AD, although the level of Αβ in the blood is the same for healthy individuals and for AD patients. Earlier, it has been shown that isomerization of aspartate 7, the most abundant post-translational modification of the Αβ peptide, is tightly involved in a set of molecular processes associated with AD progression. Therefore, the isoAsp 7-containing Αβ isomer (isoAβ) is assumed to be a potential biomarker of AD that can be identified in the blood. Here, we present an analytical mass spectrometric method for quantitative determination of the ratio of normal and isomerized Αβ fragments 1-16 in their binary mixtures, and all analytical capabilities, such as accuracy, detection limits, and sensitivity of the presented method, are determined and thoroughly discussed. On the basis of this method, an analytical approach for quantitative determination of this modification in the blood will be developed in further studies.

No abstract