DFT studies on the role of glutamate residue in the tyrosine nitration

The influence of the local environment (water, histidine, or glutamate anion) on the properties of tyrosine and the process of 3-nitrotyrosine formation with the presence of glutamate residue have been investigated in detail at the B3LYP/6-31++G(d,p) theory level. The results show that the presence of glutamate anion within a few angstroms from the tyrosine residue (a) may help the tyrosine more likely to ionize and more easily to form radical by acting as a proton acceptor; (b) may stabilize the intermolecular complex M1 and direct the nitro reagent to the two equivalent ortho carbons of the aromatic ring of tyrosine residues mainly by the N···O interaction whose geometry is found to be vertical with the plane of nitro due to the electrostatic interaction between N atom of
- NO2 and O atom of glutamate anion; (c) may assist to form the more stable complex M3 through the concerted double proton transfer, in which the glutamate residue acts as a proton switch to catalyze the proton transfer.