Fig. 3: MS/MS spectra of GMP, 15N-GMP and 13C-GMP modified peptides fragmented with HCD.
From: Mass spectrometric based detection of protein nucleotidylation in the RNA polymerase of SARS-CoV-2
a Top-scoring HCD peptide spectrum match for an EAV nsp7 peptide that is labeled close to the N-terminus with GMP. Ion series fragmentation for this peptide is illustrated. b Top-scoring HCD peptide spectrum match from an EAV nsp7 peptide that is labeled close to the N-terminus with 13C-GMP. c Top-scoring HCD peptide spectrum match from an EAV nsp7 peptide that is labeled close to the C-terminus with 15N-GMP. Note that Sequest HT assigned the 15N-GMP modification to R17, instead of the correct site at K16. Spectra are additionally labeled with guanine fragment ions and dominant peptide fragments that have lost the GMP modified plus one or two H2O molecules. Asterisks indicate the assigned GMP-modification site. Red and blue coloring indicate b- fragment ions and y- fragment ions. The GMP-modified EAV peptides were observed at least two separate experiments.
