Understanding the interactions of polysaccharides with lipids is of major importance for understanding the physicochemical properties of membranes. Among the different experimental approaches used to analyze such molecular complexes, solid-state NMR is a method of choice. However, realistic models at the atomic scale are sometimes necessary to understand the NMR spectral signatures obtained experimentally and to reveal the detailed three dimension structure of such complexes. Theoretical approaches such as classical molecular dynamics (MD) or quantum chemical methods are suitable to bring support to these studies. Before using these computational method in a routine manners, several validation steps are necessary, based on the quantum chemical calculations of 13C NMR spectra on one hand and on molecular dynamics simulations of complexation process on the other. For this purpose, several calculations have been carried out on amylose-palmitic acid complexes. First, molecular dynamic simulations using modified GLYCAM force field have been undergone using increasing degree of polymerization in order to study the complexation process as a function of amylose size. This study has revealed the minimal amylose size necessary to undertake a stable complex with lipid with characteristic V-helix structure. On a second time, based on structures extracted form MD simulations, Density Functional Theory (DFT) B3LYP using GIAO method has been employed in order to simulate 13C NMR spectra of these amylose-lipid complexes. Using full quantum strategy (DFT geometry optimization and 13C chemical shift computation), we were able to reproduce almost quantitatively the experimental spectrum of a V-type amylose complexed to a palmitic acid and to interpret all NMR signals observed experimentally. This computational strategy that combines molecular dynamics and quantum chemical calculations of NMR parameters can safely be employed to study the interactions of different polysaccharides with others lipids or with others components (DNA, proteins, …) provided we have experimental NMR data to compare to.

Polysaccharide-lipid interactions. A theroretical study using molecular dynamics simulations and quantum chemical 13C NMR spectra computation

2019 Spring National Meeting

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