Influence of Aqueous Solvation on Side Chain-Backbone Interaction in Comblike Branched Bacterial Polysaccharides

Abstract

The solution behavior of regularly repeating branched bacterial copolysaccharides has been modeled using an approximate statistical mechanical treatment that accounts for the effects of side chainbackbone interactions on the conformational freedom of the backbone glycosidic linkages. The probability distribution for glycosidic linkage orientations is based on pseudoindependent nearest-neighbor conformational energy surfaces for each backbone linkage, perturbed by the influence of the side chain-backbone interaction. The influence of aqueous solvation has been investigated by using conformational potential energy functions that incorporate strong intrapolymeric hydrogen bonding to simulate weak solvation; stronger aqueous solvation is modeled by reducing the strength of the intramolecular hydrogen bonds. This approach recognizes the geometric specificities of aqueous hydrogen-bonded solvation more realistically than do continuum approaches to solvation but is less computationally intensive than procedures (e.g., molecular dynamics) that incorporate the solvent molecules explicitly. It is shown that variations of the strength of aqueous solvation over an energetically reasonable range can have a marked influence of the solution configuration of the polysaccharide chain. Poor solvation is predicted for one paradigmatic comblike polysaccharide chain to induce an intrinsic bending anisotropy reminiscent of the intrinsic supercoiling of regularly repeating polynucleotides. be strongly modulated by the extent to which the backbone and side chain are solvated. In the present work we undertake to describe the role of aqueous solvation by

Polysaccharides in Solution: Experimental and Computational Studies

“…Conformational sampling over a nanosecond time scale, which is the current limit of solvated molecular dynamics simulations, is still far too short to adequately sample the conformational space available to a polysaccharide in solution. MD simulations may achieve considerably more sampling, and the absence of explicit water is in some way compensated for within the force ield, which may be applicable to polysaccharides [28]. Crystalline environments may be adequately sampled on much shorter time scales, and MD simulations of solid-state polysaccharides are useful in their structural and energetic interpretations [29].…”

Local Dynamics of Carbohydrates. 1. Dynamics of Simple Glycans with Different Chain Linkages

“…Hydrogen bonding between sugar hydroxyl groups has been suppressed in an effort to approximate better the intrapolymer interactions in an aqueous environment. 28 The force field employed has been described previously. 29 In all cases the allowed conformational states are reported in terms of energy maps shown in the full 2π × 2π space of the torsional variables φ and ψ for the glycan dimer in question.…”

“…The skeletal sugar residues have been taken rigidly constrained to their most stable 4 C 1 chair conformation, using averaged α- d -glucose residue coordinates found in the literature and previously used for the calculations of amylose aqueous solution properties. , All internal coordinates are fixed as the variables φ, ψ have been stepped incrementally in 10° intervals through the full angular range. Hydrogen bonding between sugar hydroxyl groups has been suppressed in an effort to approximate better the intrapolymer interactions in an aqueous environment . The force field employed has been described previously …”

Untitled

“…Conformational sampling over a nanosecond time-scale, which is the current limit of solvated MD simulations, is still far too short to adequately sample the conformational space available to a polysaccharide in solution. MC simulations may achieve considerably more sampling, and, to the extent that the absence of explicit water is in some way compensated for within the force field, these may be applicable to polysaccharides [52]. Crystalline environments may be adequately sampled on much shorter time-scales and MD simulations of solid state polysaccharides have already been useful in their structural and energetic interpretation [53].…”