posted on 2019-01-09, 00:00authored byWenhui Zhang, Reagan Meredith, Mi-Kyung Yoon, Xiaocong Wang, Robert J. Woods, Ian Carmichael, Anthony S. Serianni
NMR
studies of two 13C-labeled disaccharides and a tetrasaccharide
were undertaken that comprise the backbone of a novel thermal hysteresis
glycolipid containing a linear glycan sequence of alternating [βXylp-(1→4)-βManp-(1→4)]n dimers. Experimental trans-glycoside NMR J-couplings, parameterized equations obtained from density
functional theory (DFT) calculations, and an in-house circular statistics
package (MA’AT) were used to derive conformational
models of linkage torsion angles ϕ and ψ in solution,
which were compared to those obtained from molecular dynamics simulations.
Modeling using different probability distribution functions showed
that MA’AT models of ϕ in βMan(1→4)βXyl
and βXyl(1→4)βMan linkages are very similar in
the disaccharide building blocks, whereas MA’AT models of ψ differ. This pattern is conserved in the tetrasaccharide,
showing that linkage context does not influence linkage geometry in
this linear system. Good agreement was observed between the MA’AT and MD models of ψ with respect to mean
values and circular standard deviations. Significant differences were
observed for ϕ, indicating that revision of the force-field
employed by GLYCAM is probably needed. Incorporation of the experimental
models of ϕ and ψ into the backbone of an octasaccharide
fragment leads to a helical amphipathic topography that may affect
the thermal hysteresis properties of the glycolipid.