Protein-DNA and ion-DNA interactions revealed through contrast variation SAXS.

摘要: Understanding how DNA carries out its biological roles requires knowledge of interactions with partners. Since is a polyanionic polymer, electrostatic contribute significantly. These are mediated by positively charged protein residues or charge compensating cations. Direct detection these partners and/or their effect on conformation poses challenges, especially for monitoring conformational dynamics in real time. Small-angle x-ray scattering (SAXS) uniquely sensitive to both the and local environment (i.e. partner associated ions) DNA. The primary challenge studying multi-component systems SAXS lies resolving each component contributes measured scattering. Here, we review two contrast variation (CV) strategies that enable targeted studies structures First, solution enables measurement within protein–DNA complex masking contribution profile. We specific example, which real-time unwrapping from nucleosome core particle during salt-induced disassembly. second method, heavy atom isomorphous replacement, reports spatial distribution cation cloud around duplex exploiting changes strength cations varying atomic numbers. demonstrate application this approach provide monovalent (Na+, K+, Rb+, Cs+) standard 25-base pair CV presented here valuable tools understanding