Unravelling the structural complexity of glycolipids with cryogenic infrared spectroscopy

Carla Kirschbaum,Eike Mucha,Sandy Gewinner,Mateusz Marianski,Andreas Zappe,Kevin Pagel,Luc Teyton,Kim Greis,Gert Von Helden,Wieland Schöllkopf,Gerard Meijer,Shenglou Deng,Lisa Kain,Paul B Savage

doi:10.1038/s41467-021-21480-1

Abstract

Glycolipids are complex glycoconjugates composed of a glycan headgroup and a lipid moiety. Their modular biosynthesis creates a vast amount of diverse and often isomeric structures, which fulfill highly specific biological functions. To date, no gold-standard analytical technique can provide a comprehensive structural elucidation of complex glycolipids, and insufficient tools for isomer distinction can lead to wrong assignments. Herein we use cryogenic gas-phase infrared spectroscopy to systematically investigate different kinds of isomerism in immunologically relevant glycolipids. We show that all structural features, including isomeric glycan headgroups, anomeric configurations and different lipid moieties, can be unambiguously resolved by diagnostic spectroscopic fingerprints in a narrow spectral range. The results allow for the characterization of isomeric glycolipid mixtures and biological applications.

Highlights

Glycolipids are complex glycoconjugates composed of a glycan headgroup and a lipid moiety
In case of microbial infections, they trigger the activation of natural killer T-cells (NKT), a T cell subset sitting at the interface between innate and adaptive immunities5–8. α-galactosyl ceramides (GalCer) was first isolated as an antitumor agent from marine sponge[9] and was thought to be produced exclusively by bacteria and porifera[10]
Spectra is not impaired by impurities from biological matrices present in solution, because the glycolipid of interested is isolated in the gas phase by a mass-to-charge filter prior to measurement. This comprehensive spectroscopic study demonstrates the potential of cryogenic gas-phase IR spectroscopy for the characterization of glycolipid isomers

Summary

Introduction

Glycolipids are complex glycoconjugates composed of a glycan headgroup and a lipid moiety Their modular biosynthesis creates a vast amount of diverse and often isomeric structures, which fulfill highly specific biological functions. We investigate consistent sets of synthetic glycolipid isomers (Supplementary Table 1) using cryogenic gas-phase infrared (IR) spectroscopy in helium nanodroplets[16]. In this technique, protonated or sodiated glycolipids are generated by nano- electrospray ionization, mass-to-charge selected, pre-cooled by buffer gas cooling (80 K) and captured in superfluid helium nanodroplets. The latter function as IR-transparent cryostats with an internal temperature of 0.4 K17.

Methods

Findings

Conclusion