Cryogenic spectroscopy of biomolecular ions: From homo-chiral selection to carbohydrate analysis

While mass spectrometry (MS) has been a workhorse tool for the detection and identification of biological molecules, it is limited in its ability to determine 3-dimensional structure.  When MS is combined with ion mobility spectrometry (IMS), which determines the orientationally averaged cross section of ions as they are dragged through a static gas, one gains valuable information on the molecular shape, albeit not the precise 3-D structure.  On the other hand, adding a vibrational spectroscopic dimension to MS provides a fingerprint that is directly related to an ion’s precise conformation, particularly when measurements are performed at cryogenic temperatures.  In our laboratory, we have constructed a hybrid instrument that combines all three techniques – MS, IMS, and cryogenic ion spectroscopy (CIS).  This multidimensional approach allows one to leverage the advantages of each technique for augmenting the information available from each method separately.

This talk will focus on two specific applications of cryogenic ion spectroscopy, combined in one case with MS and in the second case with IMS-MS.  In the first, we use it to unravel the mystery of the serine octamer.  Clusters of the amino acid serine show an extremely strong “magic number” at the octamer, which is also strongly homo-chiral, and this has caused some to speculate as to its role in homochirogenesis.  However, the structure that gives rise to this selective behaviour has never been definitively determined.  We use cryogenic ion spectroscopy coupled to mass spectrometry, together with high-level quantum chemical calculations, to solve this mystery.

The second application combines cryogenic ion spectroscopy with IMS-MS to determine the primary structure of oligosaccharides, or glycans.  Glycosylation of proteins is one of the most common post-translational modifications, and the attached glycans play a fundamental role in all biological systems. Glycans attached to proteins or lipids are present at the surface of almost all cells and mediate cell-to-cell recognition and signaling, for example.  They largely govern the interaction of cells with bacteria and viruses and are central to immune response and inflammation.  Despite their importance, glycan structure is notoriously difficult to determine, because of the many different types of isomerization that can exist.  We have shown that cryogenic vibrational spectroscopy is exquisitely sensitive to even the slightest change in structure and can easily distinguish all types of glycan isomerization.  This talk will present our initial results applying this approach and explain how it could lead to high-throughput sequencing of glycans.