THE EFFECT OF LONG-RANGE ELECTROSTATIC INTERACTIONS IN SIMULATIONS OFMACROMOLECULAR CRYSTALS - A COMPARISON OF THE EWALD AND TRUNCATED LIST METHODS

Simulations of the HIV-1 protease unit cell using a 9 angstrom. cutoff , 9/18 angstrom ''twin-range'' cutoff, and full Ewald sums have been c arried out to 300 ps. The results indicate that long-range electrostat ic interactions are essential for proper representation of the HIV-1 p rotease crystal structure. The 9 angstrom simulation did not converge in 300 ps. Inclusion of a 9/18 angstrom ''twin-range'' cutoff showed s ignificant improvement. Simulation using the Ewald summation conventio n gave the best overall agreement with x-ray crystallographic data, an d showed the least internal differences in the time average structures of the asymmetric units. The Ewald simulation represents an efficient implementation of the Particle Mesh Ewald method [Darden et al., J. C hem. Phys. 98, 10 089 (1993)], and illustrates the importance of inclu ding long-range electrostatic forces in large macromolecular systems.