NMR Chemical Shift Prediction of Glycopeptides and Glycoproteins Aided by the Computer Program CASPER

In posttranslational modifications of proteins and peptides by glycosylation, the two major classes are N-linked and O-linked glycans. The sugar residue proximal to the peptide chain is in N-glycans linked to L-asparagine, and in O-linked glycans, it is linked to either L-serine, L-threonine, or L-tyrosine, although other amino acids may be glycosylated. Identifying and assigning the ¹H and ¹³C nuclear magnetic resonance (NMR) chemical shifts of these glycoconjugates are a prerequisite for structural characterization as well as for subsequent conformational and interaction studies thereof. The web-based computer program CASPER ( http://www.casper.organ.su.se/casper ) is a tool that provides prediction of ¹H and ¹³C NMR chemical shift for glycans, as well as those linked to L-Asn, L-Ser, L-Thr, or L-Tyr, for which the predicted NMR chemical shifts of the glycan show good agreement to those from NMR experiments of glycopeptides and glycoproteins. This highlights that an approximation in which a single amino acid is present at the reducing end of the glycan structure is sufficient to predict NMR data well, as shown for different N-linked and O-linked glycans of various complexity.