news

Our paper on statistical analysis and Quantum Chemical Calculation on RNA base stacks is now available on JCIM website. This fundamental contribution to understanding of RNA structures will hopefully help design better RNA folding algorithms and in the field of RNA-based drug design.  Nucleobase π–π stacking is one of the crucial organizing interactions within three-dimensional (3D) RNA architectures. Characterizing the structural variability of these contacts in RNA crystal structures will help delineate their subtleties and their role in determining function. This analysis of different stacking geometries found in RNA X-ray crystal structures is the largest such survey to date; coupled with quantum-mechanical calculations on typical representatives of each possible stacking arrangement, we determined the distribution of stacking interaction energies. A total of 1,735,481 stacking contacts, spanning 359 of the 384 theoretically possible distinct stacking geometries, were identified. Our analysis reveals preferential occurrences of specific consecutive stacking arrangements in certain regions of RNA architectures. Quantum chemical calculations suggest that 88 of the 359 contacts possess intrinsically stable stacking geometries, whereas the remaining stacks require the RNA backbone or surrounding macromolecular environment to force their formation and maintain their stability. Our systematic analysis of π–π stacks in RNA highlights trends in the occurrence and localization of these noncovalent interactions and may help better understand the structural intricacies of functional RNA-based molecular architectures. https://doi.org/10.1021/acs.jcim.2c01116

Our computational work on the interaction of Guanidinium salts with proteins is now available on PCCP’s website. This work will help better understand protein ligand binding and protein denaturation processes. In the present work, 86 available high resolution X-ray structures of proteins that contain one or more guanidinium ions (Gdm+) are analyzed for the distribution and nature of noncovalent interactions between Gdm+ and amino-acid residues. A total of 1044 hydrogen-bonding interactions were identified, of which 1039 are N–H⋯O, and five are N–H⋯N. Acidic amino acids are more likely to interact with Gdm+ (46% of interactions, 26% Asp and 20% Glu), followed by Pro (19% of interactions). DFT calculations on the identified Gdm+–amino acid hydrogen-bonded pairs reveal that although Gdm+ interacts primarily with the backbone amides of nonpolar amino acids, Gdm+ does interact with the sidechains of polar and acidic amino acids. We classified the optimized Gdm+–amino acid pairs into parallel [p], bifurcated [b], single hydrogen bonded [s] and triple hydrogen bonded [t] types. The [p] and [t] type pairs possess higher average interaction strength that is stronger than that of [b] and [s] type pairs. Negatively charged aspartate and glutamate residues interact with Gdm+ ion exceptionally tightly (−76 kcal mol−1) in [p] type complexes. This work provides statistical and energetics insights to better describe the observed destabilization or denaturation process of proteins by guanidinium salts. https://doi.org/10.1039/D2CP04943K