N-glycosylation of suboptimal sequons. (A) The STT3A and STT3B datasets were divided into deciles based on Δlog₂ values. The percentage of NXT sites in each decile is shown. (B) The distribution of amino acids at the X position of 1,263 NXT sites and 906 NXS sites plus 21 NXC sites was determined. The results are expressed as an O/E ratio. O/E ratios were calculated for the −2, −1, +1(X), +2, and +3 positions (Table S5). (C) Acceptor site flanking scores (Tables S2 B and S3 B) that were calculated as the sum of the log₂ O/E for the five residues (−2 to +3) are shown for the STT3A dataset. The number of NXT sites and NXS/C sites in half-unit bins is plotted (left panel). Glycosylation sites with a flanking score <0 (red bars) are potential suboptimal sites. (D) The distribution of suboptimal sites in each decile of the STT3A and STT3B datasets.