Electric Fields: A Metric for Molecular-level Understanding of Protein Mechanisms

Determining the molecular mechanisms at the origin of protein function remains a challenge due to the complex non-covalent interactions that shape their structure. Since the non-covalent interactions arise from charge fluctuations, electric fields can be used as a tool to quantify the interactions between a target and its environment. The contribution of each component of the system is reflected in the direction and strength of the electric field exerted on the target, which can be calculated from molecular dynamics simulations. The interactions experienced by ligands in enzymatic active sites determine the catalytic activity of the enzyme. Ligands in synthetic enzymes lack interactions with the protein scaffold, which limit their efficiency. To substitute for the role of non-effective protein scaffold, we introduced a polar DNA fragment to the enzyme vicinity, inducing electrostatic interactions that will facilitate the reaction. We found that the introduction of a DNA fragment enhanced the original interactions between the residues in the active site and the ligand, without creating new interaction hot spots. Using electric fields, we calculated a reduction in activation energy of 2.0 kcal/mol when introducing the DNA fragment, indicating a promising avenue for catalytic improvement. Inspired by the success in using electric fields to understand enzyme catalysis in the context of electrostatic preorganization theory, we generalized these fundamental concepts to another type of proteins: voltage-gated ion channels. Our results indicate that electric fields also report on channel activity. We find an asymmetry in the number of active residues for channel function between the four domains and between the two gating motifs of the permeation pathway, with domain I being the major contributor in both cases. The importance of residues for channel activity is not a simple linear correlation of their distance with the functional motif, but a relationship dominated by non-covalent interactions. Finally, we investigate the effects of loop dynamics on enzyme product inhibition. We modify the chemical nature of the unstructured loops that obstruct the active site of DszB by glycosylating serine and threonine residues. We monitor the corresponding variations in loop dynamics and their effect on the interaction between the enzyme and the product. Overall, promising results were found using electric fields in the investigation of protein mechanisms that are mainly dominated by non-covalent interactions and provide insight into the role of the individual components in the system.