Understanding the Role of R266K Mutation in Cystathionine β-Synthase (CBS) Enzyme: An in Silico Study

Human cystathionine β-synthase (hCBS) is a Heme containing unique pyridoxal 5’-phosphate (PLP) dependent enzyme that catalyzes the bio-chemical condensation reactions in the transsulfuration pathway. The role of Heme in the catalytic activities of enzyme has not yet been understood completely, even though various experimental studies have indicated its participation in the bi-directional electronic communication with the PLP center. Most probably Heme acts as the electron density reservoir for the catalytic reaction center but not as a redox electron source. Here, in this work, we investigated In Silico dynamical aspects of the bi-directional communications by performing classical molecular dynamics (MD) simulations upon developing the necessary force field parameters for the cysteine and histidine bound hexa-coordinated Heme. The comparative aspects of electron density overlap across the communicating pathways are also explored adopting the density functional theory (DFT) in conjunction with the hybrid exchange-correlation functional for the CSB^WT (wild-type) and CBS^R266K (mutated) case. The atomistic MD simulations and subsequent explorations of the electronic structures not only confirm the reported observations but provide an in-depth mechanistic understating of how the non-covalent hydrogen bonding interactions with Cys52 control such long-distance communication. Our study also provides a convincing answer to the reduced enzymatic activities in the R266K hCBS in comparison to the wild-type enzymes. We further realized that the difference in hydrogen-bonding patterns, as well as salt-bridge interactions, play a pivotal role in such long distant bi-directional communications.