Computational Evidence for the Enzymatic Transformation of 2-Hydroxypropylphosphonate to Methylphosphonate

Understanding the origins of greenhouse gas methane in the ocean is of great environmental importance, especially for global climate change and the flow of carbon within the earth surface system. A mutant (E176H) of 2-hydroxyethylphosphonate dioxygenase (HEPD) has been reported to catalyze the transformation of 2-hydroxypropylphosphonate (2-HEP) to methylphosphonate (MPn), a compound that can be easily transformed to methane by C-P lyase in a marine microbe. Here, the HEPD E176H-catalyzed transformation of 2-HEP to MPn was investigated at the molecular level using the quantum mechanics/molecular mechanics method. The results evidenced the feasibility of the transformation of 2-HEP to MPn and highlighted that the transformation contains five elementary steps: H abstraction, O-O bond cleavage, H transfer, C-C bond cleavage, and MPn formation. H abstraction was found to be the rate-determining step with an energy barrier of 17.8 kcal/mol, which is in reasonable accordance with the experimentally determined rate constant (0.38 s(-1), corresponding to 18.0 kcal/mol). Three intersystem crossing events were involved in H-abstraction, H-transfer, and MPn-formation steps. Residue electrostatic analysis on the rate-determining step suggests that proper mutation of Tyr174 may improve the enzymatic efficiency.