Inclusion of deuterated glycopeptides provides increased sequence
coverage in hydrogen/deuterium exchange mass spectrometry analysis of
SARS-CoV-2 spike glycoprotein
Abstract
Rationale. Hydrogen/deuterium exchange mass spectrometry
(HDX-MS) can provide precise analysis of a protein’s conformational
dynamics across varied states, such as heat-denatured vs. native protein
structures, localizing regions that are specifically affected by such
conditional changes. Maximizing protein sequence coverage provides high
confidence that regions of interest were located by HDX-MS, but one
challenge for complete sequence coverage is N-glycosylation sites. The
deuteration of peptides post-translationally modified by
asparagine-bound glycans (glycopeptides) has not always been identified
in previous reports of HDX-MS analyses, causing significant sequence
coverage gaps in heavily glycosylated proteins and uncertainty in
structural dynamics in many regions throughout a glycoprotein.
Methods. We detected deuterated glycopeptides with a Tribrid
Orbitrap Eclipse mass spectrometer performing data-dependent
acquisition. An MS scan was used to identify precursor ions, if
high-energy collision-induced dissociation (HCD) MS/MS of the precursor
indicated oxonium ions diagnostic for complex glycans then electron
transfer low-energy collision-induced dissociation (EThcD) MS/MS scans
of the precursor identified the modified asparagine residue and the
glycan’s mass. As in traditional HDX-MS the identified glycopeptides
were then analyzed at the MS level in samples labeled with D
2O. Results. We report HDX-MS analysis of the
SARS-CoV-2 spike protein ectodomain in its trimeric pre-fusion form,
which has 22 predicted N-glycosylation sites per monomer, with and
without heat treatment. We identified glycopeptides and calculated their
average isotopic mass shifts from deuteration. Inclusion of the
deuterated glycopeptides increased sequence coverage of spike ectodomain
from 76% to 84%, demonstrated that glycopeptides had been deuterated,
and improved confidence in results localizing structural
re-arrangements. Conclusion. Inclusion of deuterated
glycopeptides improves the analysis of the conformational dynamics of
glycoproteins such as viral surface antigens and cellular receptors.