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"Effect of Charge Distribution on the Electrostatic Chromophore-Protein
Interactions in Bacteriorhodopsin" M. NonellaJ. Comp. Chem. 18, 1997, 677-693. Abstract: Charge distributions for a protonated and unprotonated Schiff base model compound have been determined using different quantum chemical methods. After fitting the model molecule onto the protonated retinal Schiff base in Bacteriorhodopsin, electrostatic interaction energies between model molecule and protein have been calculated. Such interaction energies and, thus, also calculated pK1/2 values of the model molecule, are shown to considerably depend on the chosen charge distribution. A fairly good agreement with a calculated reference pK1/2 of this model molecule has also been found in the case of some non-potential derived charge distributions and has been shown to be caused by cancellation of errors in contributing terms. Electrostatic potential derived partial charges determined at different ab initio levels are shown to reveal interaction energies between the model molecule and proximate groups like ARG-82, ASP-85, and ASP-212, which vary by not more than 5% among the different charge distributions. Larger deviations are found in the case of Mulliken charge distributions. Based on the results of the present study we propose a new set of partial charges for the protonated and unprotonated retinal Schiff base to be used in molecular dynamics simulations and electrostatics calculations. BMO authors (in alphabetic order): Marco Nonella |