Carboxypeptidase Y from Saccharomyces cerevisiae. Conformational differences reflected in kinetic behaviour in water and deuterium oxide

Cooperative dual-stimuli-triggered aggregation of poly-L-histidine-functionalized au nanoparticles

Nanoparticles that are responsive to multiple stimuli allow more precise control over the aggregation process and thus the structures and properties of the resulting aggregates. Au nanoparticles functionalized by poly-L-histidine (PLH), a simple polypeptide with a pK(a) value (approximately 6.2) around the physiological pH, are sensitive to pH and temperature simultaneously. The dual stimuli, pH and temperature, must act in a cooperative way to switch the hydrophobic beta-sheet structure of PLH and thus trigger the assembly/disassembly of the Au nanoparticles. The aggregation process and thus the conformation change of PLH can be well recognized by the color change of the Au nanoparticles by naked eyes.

Renaturation of guanidine-unfolded tryptophan synthase by multi-mixing stopped-flow dilution in D2O

Guanidine hydrochloride (GdnHCl) at high concentrations, e.g. 4 to 8 M, has been used extensively to promote reversible denaturation of several proteins. The refolding is induced by removal of the denaturing agent by diluting the denatured protein at least 50-100-fold in a 'renaturation buffer'. Fast kinetic studies, using a stopped-flow apparatus to achieve such dilutions, are difficult for two reasons: firstly, injecting widely different volumes of the two reagents does not afford a proper mixing. Secondly, the density differences existing between the concentrated GdnHCl solution and the renaturation buffer often causes important mixing and redistribution artefacts particularly in vertical stopped-flows. Here, it is shown that these difficulties can be overcome by using a multi-mixing stopped-flow to achieve 2 successive 7-fold dilutions and by using heavy water (D2O) to adjust the density of the renaturation buffer. This enabled us to study the appearance of a short-lived intermediate during the folding of the beta 2-subunit of Escherichia coli tryptophan synthase.

Hypersensitivity to heavy water: a new conditional phenotype

Wild-type strains of the yeast S. cerevisiae can grow on media containing 90% D2O. Using chemical mutagenesis we obtained a number of strains that grow on H2O-containing media but not on otherwise identical media containing 90% D2O. The frequency of these D2O-sensitive (d) mutants is comparable to the frequency of conventional temperature-sensitive (ts) mutants in the same mutagenized sample, and the ds mutations are distributed over a large number of complementation groups. Furthermore, most ds mutants do not display other conditional phenotypes, such as heat, cold, or osmotic sensitivity. Conversely, of 17 cell division cycle ts mutants tested, only 2 are also ds. Thus, the ds technique should be useful for producing conditional mutations in genes that are not amenable to the ts and cs approaches, and also for generating alternative conditional (ds) alleles in many other genes. In addition, the ds technique should make it possible to generate conditional (ds) mutants in homeothermic animals, thereby extending the advantages of conditional phenotypes to mammalian and avian genetics.