A FORCE-FIELD FOR MONOSACCHARIDES AND (1-]4)-LINKED POLYSACCHARIDES

A force field for monosaccharides that can be extended to (1 --> 4) linked polysaccharides has been developed for the AMBER potential function. The resulting force field is consistent with the existing AMBER force field for proteins and nucleic acids. Modifications to the standard AMBER OH force constant and to the Lennard-Jones parameters were made. Furthermore, a 10-12 nonbonded term was included between the hydroxyl hydrogen of the saccharide and the water oxygen (TIP3P, SPC/E, etc.) to reproduce better the water-saccharide intermolecular distances. STO-3G electrostatic potential (ESP) charges were used to represent the electrostatic interactions between the saccharide and its surrounding environment. To obtain charges for polysaccharides, a scheme was developed to piece together saccharide residues through 1 --> 4 connections while still retaining a net neutral charge on the molecule as a whole. Free energy perturbation (FEP) simulations of D-glucose and D-mannose in water were performed to test the resulting force field. The FEP simulations demonstrate that AMBER overestimates intramolecular interaction energies, suggesting that further improvements are needed in this part of the force field. To test further the reliability of the parameters, a molecular dynamics (MD) simulation of alpha-D-glucose in water was also performed. The MD simulation was able to produce structural and conformational results that are in accord with experimental evidence and previous theoretical results. Finally, a relaxed conformational map of beta-maltose was assembled and it was found that the present force field is consistent with available theoretical and experimental results. (C) 1994 by John Wiley and Sons, Inc.