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abstracts
A typical protein crystal contains 30-60% solvent. For a naked crystal, this solvent is distributed between solvent shells, where water and solvent molecules make specific interactions with the crystalline protein, and solvent channels filled with disordered solvent molecules. This internal solvent map of the crystal can be modified by placing the crystal in a dehydrating environment. This may in turn induce changes to the crystal lattice and affect mosaicity, resolution and quality of diffraction data. A dehydrating environment can be generated around a crystal in several ways with various degrees of precision and complexity. In this study we have used the HC1 device (Maatel) to mount crystals an air stream of known relative humidity - a precise yet hassle-free approach to altering crystal hydration. We set out to analyse a range of different crystals to establish usable protocols that will allow one to explore to crystal hydration space, either by preparing samples before synchrotron beamtime or by undertaking the experiments during beamtime. Our results, considered in the light of the literature surrounding crystal dehydration, provide guidance for when dehydration can help diffraction.
abstracts
Since the 1980s, there has been great interest in how polypyridyl ruthenium complexes bind to DNA. This is due to their photoactive properties[1], which have great potential in photodynamic therapy, as they are able to damage DNA upon photoirradiation. However, there has been significant debate over the precise binding sites of these complexes due to the lack of definitive structural information. Presented here are several high resolution crystal structures showing how these complexes can bind to short DNA oligonucleotides. With each new structure we are able to answer questions about the binding geometry and step specificity which could explain the observations obtained from biophysical measurements in solution. We have shown that the complexes bind by intercalation as well as confirming a previously proposed binding mode, semi-intercalation. We have also shown that the complexes bind with a high level of sequence specificity[2], preferring TA steps over AT and CG and that each enantiomer can bind with a different orientation[3] (Figure 1). One obvious advantage to working with crystal samples is that they possess a well defined molecular structure, which can be determined and is therefore known. Spectroscopic experiments, with data collected in the picosecond and nanosecond timescale, will also be reported with these systems.
