RNA sampling and crystallographic refinement using Rappertk

Background. Dramatic increases in RNA structural data have made it possible to recognize its conformational preferences much better than a decade ago. This has created an opportunity to use discrete restraint-based conformational sampling for modelling RNA and automating its crystallographic refinement. Results. All-atom sampling of entire RNA chains, termini and loops is achieved using the Richardson RNA backbone rotamer library and an unbiased distribution for glycosidic dihedral angle. Sampling behaviour of Rappertk on a diverse dataset of RNA chains under varying spatial restraints is benchmarked. The iterative composite crystallographic refinement protocol developed here is demonstrated to outperform CNS-only refinement on parts of tRNA(Asp) structure. Conclusion. This work opens exciting possibilities for further work in RNA modelling and crystallography.