Effect of charge distribution on electrostatic chromophore?protein interactions inBacteriorhodopsin

✍ Scribed by Nonella, Marco

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 328 KB
• Volume: 18
• Category: Article
• ISSN: 0192-8651
• DOI: 10.1002/(sici)1096-987x(19970415)18:5<677::aid-jcc8>3.0.co;2-k

✦ Synopsis

Charge distributions of a protonated and unprotonated Schiff base model compound are determined using different quantum chemical methods. After fitting the model molecule onto the protonated retinal Schiff base in Bacteriorhodopsin, electrostatic interaction energies between the model molecule and protein are calculated. Interaction energies as well as the calculated p K 1r2 values of the model molecule are shown to depend considerably on the chosen charge distribution. Electrostatic potential derived partial charges determined at different ab initio levels reveal interaction energies between the model molecule and nearby residues such as ARG-82, ASP-85, and ASP-212, which are relatively method independent. Consequently, such charge distributions also result in p K values for the model molecule that are very similar. Larger deviations in 1r2 the electrostatic interaction energies, however, are found in the case of charge distributions derived according to the Mulliken population analysis. Nevertheless, some sets of Mulliken derived partial charges predicted p K 1r2 values for the model molecule that are close to those determined with electrostatic potential derived partial charges. This agreement, however, is only achieved because the individual errors of the contributing terms are approximately compensated. The use of the extended atom model is shown to be problematic. Although potential derived charges can correctly describe electrostatic interaction energies, they fail to predict p K values. On the basis 1r2 of the present investigation a new set of partial charges for the protonated and unprotonated retinal Schiff base is proposed to be used in molecular dynamics simulations and electrostatics calculations.