PubMed · 14018330
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
P CANNON. 1963. Cold immersion.. https://pubmed.ncbi.nlm.nih.gov/14018330/
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
Cold-shock proteins of the CspA family help bacterial cells to acclimate to low temperatures. Some Csps bind single-stranded nucleic acids and destabilize nucleic acid secondary structures in vitro, and act as transcription antiterminators in vivo and in vitro. Nucleic acid melting by Escherichia coli CspE is critical for its ability to support low-temperature survival of the cell. Here, we explore the molecular mechanism of nucleic acid melting using CspE mutants harboring substitutions in surface-exposed residues critical for this function. Analysis of the mutants identifies two intermediates of the melting pathway and shows that CspE Phe17 and Phe30 act at the earliest stages of melting, while His32 acts later and is necessary for the propagation of melting. The results allow us to orient a CspE molecule relative to the melting substrate and to put forward a mechanistic model of nucleic acid melting by Csps.
This study, for the first time, demonstrates that it is possible to mechanically align lipid bilayers at a very low temperature (as low as the gel-to-liquid crystalline phase transition temperature). Performing NMR experiments on mechanically aligned lipid bilayers at a low temperature increases the signal-to-noise ratio, the resolution, and the span of NMR parameters. The increased lifetime of the alignment and the nature of the bilayer sample would enhance the application of solid-state NMR techniques to study membrane proteins.
Macromolecular crystals are usually cooled to approximately 100 K for X-ray diffraction experiments in order to diminish lattice damage arising from the ionizing radiation. Such cooling often produces lattice disorder, but this disorder can sometimes be substantially reduced by cycling the crystal between low and higher temperatures (called annealing). Here, two related aspects of cryocooling and annealing are investigated using crystals of beta-galactosidase and thermolysin. Firstly, as has been reported with other systems, there is an optimal cryoprotectant concentration above and below which diffraction is poor, with high mosaicity, diffuse scatter and low signal to noise. Measurements of the bulk density of the respective cryosolvents are consistent with the idea that at the optimal cryoprotectant concentration the contraction of the bulk solvent on cooling largely compensates for the contraction of the macromolecular lattice. Secondly, by controlling the relative humidity of the gas that contacts the crystal during the high (room) temperature phase, it is found that water is either imported into or exported out of the crystals during the melting phase of annealing. This water transport appears to change the concentration of the cryoprotectant solution and in so doing alters its thermal contraction. Thus, annealing appears to be involved, at least in part, in the tuning of the thermal contraction of the bulk solvent to best compensate for lattice contraction. Furthermore, it is found that if the cryoprotectant concentration is initially too high then annealing is more successful than if the concentration is initially too low. This result suggests that the search for optimal cryoprotectant conditions may be facilitated by equilibration of the crystal to relatively high cryoprotectant concentration followed by annealing.