Purification, crystallization and preliminary crystallographic analysis of DR0248, an MNT–HEPN fused protein fromDeinococcus radiodurans

DR0248 is a protein identified in theDeinococcus radiodurans(DR) genome that is predicted to encompass two domains: an N-terminal minimal nucleotidyl transferase domain (MNT) and a C-terminal higher eukaryotes and prokaryotes nucleotide-binding domain (HEPN). These two domains, usually encoded in two ORFs, have been suggested to play the role of a toxin–antitoxin (TA) system in prokaryotes. Recombinant DR0248 was overexpressed and purified fromEscherichia coliand diffraction-quality crystals were obtained in the presence of the detergent molecules dodecyldimethylamine oxide (DDAO) and octaethylene glycol monododecyl ether (C12E8), which were used as crystallization additives. Crystals grown with DDAO diffracted to a resolution of 2.24 Å and belonged to space groupC2221, with unit-cell parametersa= 98.4,b= 129.9,c= 59.2 Å. Crystals grown with C12E8 diffracted to a resolution of 1.83 Å and belonged to space groupP212121, with unit-cell parametersa= 51.6,b= 87.2,c= 108.2 Å. The structure was solved by multiwavelength anomalous dispersion from zinc bound to the protein using a single crystal obtained in the presence of DDAO.

Solubilisation of camptothecin by nonionic surfactants and alkyldimethylamine oxides

The solubilisation of poorly soluble antineoplastic drug camptothecin by nonionic surfactants (polysorbates and octylphenol ethoxylates) and alkyldimethylamine oxide surfactants with the alkyl chain length 8 to 16 carbon atoms was investigated. The hydrophobicity of the solubilising agent turned out to be the primary structural parameter controlling the solubility efficiency of camptothecin in an aqueous solution. The quantitative parameter of solubilisation (drug loading coefficient) provided values in the range of 0.1–1.2% and 0.1–1.0% for alkyldimethylamine oxides and nonionic surfactants, respectively. The decreasing number of oxyethylene units and the extension of the hydrophobic part of nonionic surfactant molecule resulted in the increase of camptothecin solubility. From the dynamic light scattering measurements, the hydrodynamic diameter values of camptothecin-loaded alkyldimethylamine oxide and nonionic micelles were found in the range of 4–42 nm and 5–120 nm, respectively. The experimental values confirmed the increase in micellar size with the increasing alkyl chain length. The values of the packing parameter of camptothecin-loaded dodecyldimethylamine oxide micelles indicate their spherical shape at all the investigated surfactant concentrations. A simple computer model of camptothecin-loaded dodecyldimethylamine oxide micelle provided the diameter of the structure cross section which is consistent with the experimental values.