| Abstract
| - The molecular electrostatic potential inside the potassium channel protein from Streptomyces lividans hasbeen investigated using linear scaling semiempirical quantum chemical method, for a variety of geometries,with and without solvating water molecules. The results are compared with those given by a number ofpopular molecular mechanics force-fields. The difference between the quantum and molecular mechanicselectrostatic potentials due to the protein exceeds 30 kcal/mol within the narrow selectivity filter of the channeland is attributed to the neglect of electronic effects, e.g., polarization, in the molecular mechanics force-fields. In particular, mutual electronic interactions between four threonine residues in the selectivity filter arefound to have a large effect on the electrostatic potential. Calculations in the presence of water moleculessuggest that molecular mechanics methods also overestimate the stabilization of the cation inside the ionchannel. The molecular electrostatic potentials computed by molecular mechanics force-fields expressed relativeto bulk water, however, reveal a much smaller error.
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