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- W2315039862 endingPage "936" @default.
- W2315039862 startingPage "927" @default.
- W2315039862 abstract "The mechanism of the backbone cleavage-transesterification step of the RNase A enzyme remains controversial even after 60 years of study. We report quantum mechanics/molecule mechanics (QM/MM) free energy calculations for two optimized reaction paths based on an analysis of all structural data and identified by a search for reaction coordinates using a reliable quantum chemistry method (B3LYP), equilibrated structural optimizations, and free energy estimations. Both paths are initiated by nucleophilic attack of the ribose O2′ oxygen on the neighboring diester phosphate bond, and both reach the same product state (PS) (a O3′–O2′ cyclic phosphate and a O5′ hydroxyl terminated fragment). Path 1, resembles the widely accepted dianionic transition-state (TS) general acid (His119)/base (His12) classical mechanism. However, this path has a barrier (25 kcal/mol) higher than that of the rate-limiting hydrolysis step and a very loose TS. In Path 2, the proton initially coordinating the O2′ migrates to the nonbridging O1P in the initial reaction path rather than directly to the general base resulting in a triester (substrate as base) AN + DN mechanism with a monoanionic weakly stable intermediate. The structures in the transition region are associative with low barriers (TS1 10, TS2 7.5 kcal/mol). The Path 2 mechanism is consistent with the many results from enzyme and buffer catalyzed and uncatalyzed analog reactions and leads to a PS consistent with the reactive state for the following hydrolysis step. The differences between the consistently estimated barriers in Path 1 and 2 lead to a 1011 difference in rate strongly supporting the less accepted triester mechanism." @default.
- W2315039862 created "2016-06-24" @default.
- W2315039862 creator A5004844824 @default.
- W2315039862 creator A5023443683 @default.
- W2315039862 creator A5084863154 @default.
- W2315039862 date "2014-01-10" @default.
- W2315039862 modified "2023-10-02" @default.
- W2315039862 title "QM/MM Simulation (B3LYP) of the RNase A Cleavage-Transesterification Reaction Supports a Triester A<sub>N</sub> + D<sub>N</sub> Associative Mechanism with an O2′ H Internal Proton Transfer" @default.
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