Primary Structure of Glycans by NMR Spectroscopy

Abstract

Glycans, carbohydrate molecules in the realm of biology, are present as biomedically important glycoconjugates and a characteristic aspect is that their structures in many instances are branched. In determining the primary structure of a glycan, the sugar components including the absolute configuration and ring form, anomeric configuration, linkage(s), sequence, and substituents should be elucidated. Solution state NMR spectroscopy offers a unique opportunity to resolve all these aspects at atomic resolution. During the last two decades, advancement of both NMR experiments and spectrometer hardware have made it possible to unravel carbohydrate structure more efficiently. These developments applicable to glycans include, inter alia, NMR experiments that reduce spectral overlap, use selective excitations, record tilted projections of multidimensional spectra, acquire spectra by multiple receivers, utilize polarization by fast-pulsing techniques, concatenate pulse-sequence modules to acquire several spectra in a single measurement, acquire pure shift correlated spectra devoid of scalar couplings, employ stable isotope labeling to efficiently obtain homo-and/or heteronuclear correlations, as well as those that rely on dipolar cross-correlated interactions for sequential information. Refined computer programs for NMR spin simulation and chemical shift prediction aid the structural elucidation of glycans, which are notorious for their limited spectral dispersion. Hardware developments include cryogenically cold probes and dynamic nuclear polarization techniques, both resulting in enhanced sensitivity as well as ultrahigh field NMR spectrometers with a 1 H NMR resonance frequency higher than 1 GHz, thus improving resolution of resonances. Taken together, the developments have made and will in the future make it possible to elucidate carbohydrate structure in great detail, thereby forming the basis for understanding of how glycans interact with other molecules.

Mapping the Acetylamino and Carboxyl Groups on Glycans by Engineered α-Hemolysin Nanopores

“…Unambiguous characterization of glycan chemical information remains a remarkable challenge. , Unlike other techniques that provide information on chemical shifts or peak intensities, , we collected glycan information from current characteristics and summarized the features for functional groups, which could directly relate how molecular structure correlates with sensing events. These findings are a step forward toward cracking the “sugar code”.…”

“…However, the analysis of functional modifications occurring in complex glycans, especially the structures containing repeating units, by the NMR method is very demanding. 17 LC−MS (liquid chromatography−MS) technology could provide the exact mass of analytes with trace samples in a short time. Nevertheless, this technology always lost the stereochemical information when applied to monosaccharides analysis.…”

“…For example, NMR can theoretically discriminate atoms in different chemical environments. However, the analysis of functional modifications occurring in complex glycans, especially the structures containing repeating units, by the NMR method is very demanding . LC–MS (liquid chromatography–MS) technology could provide the exact mass of analytes with trace samples in a short time.…”

Ultramicro and ultrasensitive detection of lipopolysaccharides based on triple-signal amplification via ultrafast ATRP and an ultramicroelectrode

“…1,2 LPS can be divided into three distinct regions: core polysaccharides, o-specific antigens, and a unique lipidpart structure called lipid A. 3 Lipid A is the main cause of toxicity of LPS, which makes LPS known as an endotoxin and can lead to fatal diseases such as septic shock, lung cancer, gastric cancer, etc. [4][5][6] According to the US Food and Drug Administration (FDA) guidelines, LPS in intraocular delivered gene therapy drugs should not exceed 0.5 EU per mL per eye (∼500 pg per mL per eye).…”

The Structure Determination of Organic Molecules by Co-crystallization of Anthracene-Based Crystallization Chaperone

“…Whether the organic compounds are natural products − or synthesized by chemists, it is extremely important to determine their structures and absolute conformations at the atomic level. Over the past few decades, numerous researchers have developed and refined many methods for the structural identification of organic molecules, such as nuclear magnetic resonance ( NMR ), − infrared spectroscopy ( IR ), − mass spectrometry ( MS ), − single crystal X-ray diffraction ( X-ray SCD ), − etc. Among them, X-ray SCD can provide direct and accurate structural information and is globally recognized as a fairly reliable method for the structural identification of organic compounds, including their stereochemical conformation.…”