Modeling conformational changes in alginic acid oligomers induced by external forces.

Area of Science:

• Biophysics
• Polymer Science
• Computational Chemistry

Background:

• Alginate oligomers are polysaccharides with varying ratios of mannuronic (M) and guluronic (G) acid units.
• The mechanical properties and conformational transitions of alginates are crucial for their applications.
• Understanding these transitions under force is key to characterizing natural alginate heterogeneity.

Purpose of the Study:

• To investigate the mechanism and nature of mechanical force-induced conformational transitions in alginate oligomers.
• To explore the influence of the G:M ratio and glycosidic linkage types on these transitions.
• To provide insights relevant for atomic force microscopy (AFM) based determination of alginate composition.

Main Methods:

• Utilized quantum mechanics (QM) at the DFT level with the Enforced Geometry Optimization (EGO) approach.
• Employed molecular dynamics (MD) simulations with hybrid interaction potentials (QM/MM).
• Characterized structural and energetic properties of conformational transitions under external mechanical forces.

Main Results:

• Observed qualitatively different responses to applied force based on the G:M ratio.
• Identified differing topologies of glycosidic linkages in G and M units as the source of varied responses.
• Determined energies of initial, final, and intermediate states during forced conformational transitions.

Conclusions:

• The G:M ratio significantly dictates the mechanical response of alginate oligomers.
• Glycosidic linkage topology plays a critical role in force-induced conformational changes.
• Results support the potential of AFM for analyzing the composition of heterogeneous alginate chains.