The Incorporation of Labile Protons into Multidimensional NMR Analyses: Glycan Structures Revisited
Mihajlo Novakovic, Marcos D. Battistel, Hugo F. Azurmendi, Maria Grazia Concilio, Darón I. Freedberg, Lucio Frydman
Abstract
Hs that undergo fast exchange with water. This study shows that even larger enhancements can be obtained for rapidly exchanging OHs in saccharides, leading to the retrieval of previously undetectable 2D TOCSY/NOESY cross-peaks with nonlabile protons. After demonstrating ≥300% signal enhancements on model monosaccharides, these experiments were applied at 1 GHz to elucidate the structural network adopted by a sialic acid homotetramer, used as a model for α,2-8 linked polysaccharides. High-field L-PROSY NMR enabled these studies at higher temperatures and provided insight previously unavailable from lower-field NMR investigations on supercooled samples, involving mostly nonlabile nuclei. Using L-PROSY's NOEs and other restraints, a revised structural model for the homotetramer was obtained combining rigid motifs and flexible segments, that is well represented by conformations derived from 40 μs molecular dynamics simulations.