Characterizing Protein Conformational Space Using Robotics-Based Search and Topological Data Analysis

Investigating the conformational space of proteins is essential in order to associate their structures with their fundamental functions. Nonetheless, it is a challenging task, both experimentally and computationally. Because of the transient nature of these conformational changes and the fact that they are impermanent, empirical methods have fallen short to capture them. In silico methods, on the other hand, have shown great promise in exploring these conformational pathways. In this article, we provide an extensive evaluation of our previously introduced, robotics inspired conformational search algorithm (RRT* with Monte Carlo). We then identify what intermediate conformations appear the most in our generated conformational pathways using TDA Mapper, a topological data analysis algorithm, and examine how close these intermediate conformations are to existing experimental data.

Analysis of the Structural Mechanism of ATP Inhibition at the AAA1 Subunit of Cytoplasmic Dynein-1 Using a Chemical “Toolkit”

Dynein is a ~1.2 MDa cytoskeletal motor protein that carries organelles via retrograde transport in eukaryotic cells. The motor protein belongs to the ATPase family of proteins associated with diverse cellular activities and plays a critical role in transporting cargoes to the minus end of the microtubules. The motor domain of dynein possesses a hexameric head, where ATP hydrolysis occurs. The presented work analyzes the structure–activity relationship (SAR) of dynapyrazole A and B, as well as ciliobrevin A and D, in their various protonated states and their 46 analogues for their binding in the AAA1 subunit, the leading ATP hydrolytic site of the motor domain. This study exploits in silico methods to look at the analogues’ effects on the functionally essential subsites of the motor domain of dynein 1, since no similar experimental structural data are available. Ciliobrevin and its analogues bind to the ATP motifs of the AAA1, namely, the walker-A (W-A) or P-loop, the walker-B (W-B), and the sensor I and II. Ciliobrevin A shows a better binding affinity than its D analogue. Although the double bond in ciliobrevin A and D was expected to decrease the ligand potency, they show a better affinity to the AAA1 binding site than dynapyrazole A and B, lacking the bond. In addition, protonation of the nitrogen atom in ciliobrevin A and D, as well as dynapyrazole A and B, at the N9 site of ciliobrevin and the N7 of the latter increased their binding affinity. Exploring ciliobrevin A geometrical configuration suggests the E isomer has a superior binding profile over the Z due to binding at the critical ATP motifs. Utilizing the refined structure of the motor domain obtained through protein conformational search in this study exhibits that Arg1852 of the yeast cytoplasmic dynein could involve in the “glutamate switch” mechanism in cytoplasmic dynein 1 in lieu of the conserved Asn in AAA+ protein family.

Efficient Generative Modelling of Protein Structure Fragments using a Deep Markov Model

Fragment libraries are often used in protein structure prediction, simulation and design as a means to significantly reduce the vast conformational search space. Current state-of-the-art methods for fragment library generation do not properly account for aleatory and epistemic uncertainty, respectively due to the dynamic nature of proteins and experimental errors in protein structures. Additionally, they typically rely on information that is not generally or readily available, such as homologous sequences, related protein structures and other complementary information. To address these issues, we developed BIFROST, a novel take on the fragment library problem based on a Deep Markov Model architecture combined with directional statistics for angular degrees of freedom, implemented in the deep probabilistic programming language Pyro. BIFROST is a probabilistic, generative model of the protein backbone dihedral angles conditioned solely on the amino acid sequence. BIFROST generates fragment libraries with a quality on par with current state-of-the-art methods at a fraction of the run-time, while requiring considerably less information and allowing efficient evaluation of probabilities.

Elucidation of Structural Mechanism of ATP Inhibition at the AAA1 Subunit of Cytoplasmic Dynein 1 Using a Chemical "Toolkit"

Dynein is a cytoskeletal motor protein that carries organelles via retrograde transport in eukaryotic cells. The motor protein belongs to the ATPase family of proteins associated with diverse cellular activities and plays a critical role in transporting cargoes to the minus end of the microtubules. The motor domain of dynein possesses a hexameric head, where ATP hydrolysis occurs. The AAA1 binding site is the leading ATP hydrolytic site, followed by the AAA3 subsite. Small-molecule ATP competitive inhibitors of dynein are thought to target the AAA1 site. The presented work elucidates the structure-activity relationship of dynapyrazole A and B, ciliobrevin A and D in their various protonated states and their 46 analogs for their binding properties in the nucleotide-binding site of the AAA1 subunit and their effects on the functionally essential subsites of the motor domain of cytoplasmic dynein 1, as there is currently no similar experimental structural data available. Ciliobrevin and its analogs bind to the ATP motifs of the AAA1, namely the Walker-A or P-loop, the Walker-B, and the sensor I and II. Ciliobrevin A shows a better binding affinity to the AAA1 binding site of dynein 1 than its D analog. Although the double bond in ciliobrevin A and D was expected to decrease the ligand potency, they show a better affinity to the AAA1 binding site than dynapyrazole A and B, lacking the bond. Protonation of the nitrogen in ciliobrevin A, D, dynapyrazole A, and B at the N9 site of ciliobrevin, and the N7 of the latter increased their binding affinity. Exploring ciliobrevin A geometrical configuration suggests the E isomer has a superior binding profile over the Z due to binding at the critical ATP motifs. Utilizing the refined structure of the motor domain obtained through protein conformational search in this study exhibits that Arg1852 of the yeast cytoplasmic dynein could involve in the "glutamate switch" mechanism in cytoplasmic dynein 1 in lieu of the conserved Asn in AAA+ protein family, as the guanidine moiety of the Arg engages in an H-bond with the carboxylate moiety of Glu1849.

Benchmark ab initio proton affinity of glycine

A systematic conformational search reveals three N- (amino) and eight O- (carbonyl) protonated glycine conformers with benchmark equilibrium(adiabatic) relative energies in the 0.00−7.51(0.00−7.37) and 25.91−31.61(24.45−30.28) kcal/mol ranges, respectively. Benchmark ab...

Boron – Noble Gas Covalent Bond in Borenium and Boronium compounds

The capability of the BH2+ parent cation to bind noble gases (Ng) has been evaluated. The results show its potential to form Borenium (BH2Ng+) and Boronium (BH2Ng2+) cations. Conformational search...