The objective of the study was to develop Karplus equations especially for the ω-angle in 1,6-linked oligosaccharides. Oligosaccharides are important in biochemical processes central to disease and can be equally important to the human body’s response to such disease. The possible constitutions and configurations allow for great structural diversity. Conformation adds additional structural complexity, namely spatial flexibility specifically at the glycosidic linkage. This type of flexibility influences the glycans’ biochemistry and thus how they act in biochemical processes. Conformational analysis of the glycosidic linkage is achieved by many different methods including NMR spectroscopy (with NOE and quantitative coupling constant measurements) and MD simulations. The Karplus equation gives an empirical relationship between the NMR coupling constant and the dihedral angle. The ω-angle in 1,6-linked oligosaccharides has only a few such Karplus equations, to our knowledge. Experimental 1H-13C-coupling constants were first extracted from JHMBC experiments. Gaussian ’09 single point NMR calculation of coupling constants were fitted to K arplus equations of the form J = Acos2(θ)+Bcos(θ)+C and J = Acos2(θ+D)+Bcos(θ+E)+C to obtain the Karplus equation. The desired dihedral angle trajectory was also extracted from MD simulations done in AMBER 14, using the GLYCAM06 force field. Subsequently, the Karplus equation was weighted by dihedral angle histograms from that trajectory to obtain the computed coupling constant. Preliminary data showed good fit between computed and experimental coupling constants in various 1,6-linked oligosaccharides.

New Karplus Equations for α-1,6-linked Glycans

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.