Radou, G. | bioRxiv Science

bioRxiv2020

Detecting genetic variation and base modifications together in the same single molecules of DNA and RNA at base pair resolution using a magnetic tweezer platform.

Accurate decoding of nucleic acid variation is important to understand the complexity and regulation of genome function. Here we introduce a single-molecule platform based on magnetic tweezer (MT) technology that can identify and map the positions of sequence variation and multiple base modifications together in the same single molecules of DNA or RNA at single base resolution. Using synthetic templates, we demonstrate that our method can distinguish the most common epigenetic marks on DNA and RNA with high sensitivity, specificity and precision. We also developed a highly specific CRISPR-Cas enrichment strategy to target genomic regions in native DNA without amplification. We then used this method to enrich native DNA from E. coli and characterized the differential levels of adenine and cytosine base modifications together in molecules of up to 5 kb in length. Finally, we enriched the 5 UTR of FMR1 from cells derived from a Fragile X carrier and precisely measured the repeat expansion length and methylation status of each molecule. These results demonstrate that our platform can detect a variety of genetic, epigenetic and base modification changes concomitantly within the same single molecules.

genomics↗

bioRxiv2018

Hydrogen exchange protection factors can be extracted from sparse HDX-MS data

Hydrogen/deuterium exchange (HDX) monitored by mass spectrometry (MS) is a promising technique for rapidly fingerprinting structural and dynamical properties of proteins. The time dependent change in mass of any fragment of the polypeptide chain depends uniquely on the rate of exchange of its amide hydrogens but determining the latter from the former is generally not possible. Here we show that, if time-resolved measurements are available for a number of overlapping peptides that cover the whole sequence, rate constants for each amide hydrogen exchange (or equivalently, their protection factors) can be predicted. In most cases, the solution may not be unique, so a number of solutions have to be considered. Such analysis always provides meaningful constraints on protection factors and thus can be used in situations where obtaining more refined data is impractical, e.g., high throughput structure and interaction fingerprinting. It also provides a systematic way to improve data collection strategies in order to obtain unambiguous information at single residue level, e.g. for assessing protein structure predictions at atomistic level.

biophysics↗