Influence of the Molecular Environment on Phosphorylated Amino Acid Models: A Density Functional Theory Study

A protein environment can affect the structure and charge distribution of substrate molecules. Here, the structure and partial charges were studied for different phosphorylated amino acid models in varying environments using density functional theory. The three systems investigated, acetyl phosphate, methyl phosphate, and p-tolyl phosphate are representative models for aspartyl phosphate, serine or threonine phosphate, and tyrosine phosphate, respectively. Combined with the CPCM continuum model, explicit HF and H₂O molecules were added in order to model environmental effects and interactions that may occur in a protein matrix. We show how the different interactions affect the scissile P–O­(R) bond and that the elongation can be explained by an anomeric effect. An increasing scissile bond length will result in transfer of negative charge to the leaving group and in a widening of the angle between the terminal oxygens of the phosphate molecule, features that can expose the phosphate group to attacking nucleophiles. Lastly, calculations were performed on the active site of the Ca²⁺-ATPase E2P intermediate, which provide an example of how a protein environment facilitates the formation of a destabilized ground state.