Self-assembled DNA crystals: the impact on resolution of 5'-phosphates and the DNA source

Designed self-assembled DNA crystals consist of rigid DNA motifs that are held together by cohesive sticky-ended interactions. A prominent application of such systems is that they might be able to act as macromolecular hosts for macromolecular guests, thereby alleviating the crystallization problem of structural biology. We have recently demonstrated that it is indeed possible to design and construct such crystals and to determine their structures by X-ray diffraction procedures. To act as useful hosts that organize biological macromolecules for crystallographic purposes, maximizing the resolution of the crystals will maximize the utility of the approach. The structures reported so far have diffracted only to about 4 Å, so we have examined two factors that might have impact on the resolution. We find no difference in the resolution whether the DNA is synthetic or PCR-generated. However, we find that the presence of a phosphate on the 5'-end of the strands improves the resolution of the crystals markedly.