Table 1.

NXT acceptor sites in eukaryotic glycoproteins

Organism Sequons (observed/expected) Glycan density Apparent modification frequency 
 T-sequon C-sequon C-glycan/T-glycan T-glycan/T-sequon C-glycan/C-sequon 
    % % 
S. cerevisiae 1.8 1.3 0.78 42 47 
S. pombe 1.6 1.7 1.15 34 38 
C. elegans 1.6 1.5 0.82 38 31 
A. thaliana 2.0 1.4 0.73 32 34 
D. melanogaster 1.6 1.3 0.74 39 38 
D. rerio 1.7 1.2 0.77 31 33 
M. musculus 1.9 1.2 0.56 44 37 
Organism Sequons (observed/expected) Glycan density Apparent modification frequency 
 T-sequon C-sequon C-glycan/T-glycan T-glycan/T-sequon C-glycan/C-sequon 
    % % 
S. cerevisiae 1.8 1.3 0.78 42 47 
S. pombe 1.6 1.7 1.15 34 38 
C. elegans 1.6 1.5 0.82 38 31 
A. thaliana 2.0 1.4 0.73 32 34 
D. melanogaster 1.6 1.3 0.74 39 38 
D. rerio 1.7 1.2 0.77 31 33 
M. musculus 1.9 1.2 0.56 44 37 

An observed/expected ratio >1 indicates positive selection for NXT sequons. T-sequon, total NXT sequons; C-sequon, NXT sequons in the C-terminal region (70 ± 5 residues). The C-sequon density (NXT sequons/1,000 residues) for the C-terminal region was calculated from linear regression fits of plots of NXT sequons versus C-terminal distance. Expected sequon densities were calculated using the amino acid composition of the glycoproteins from each species. The density (glycans/1,000 residues) of NXT glycans in the C-terminal segment (70 ± 5 residues) of proteins was determined by linear regression of plots of NXT glycopeptides versus C-terminal distance. C-glycans, C-terminal glycans; T-glycans, total glycans. The apparent modification frequency was calculated by dividing the glycan density by the sequon density. The apparent modification frequency underestimates the actual percent modification caused by incomplete detection of all glycopeptides by mass spectrometry.

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