Additional file 3: Figure S3. Peptide probe motifs that are associated with ageing and BMI. (A) Peptide sequences that are associated with age, scatter plot same as in Fig. 1d. (B) Peptide sequences that are associated with BMI. (C) Sequence motifs in peptide probes associated with BMI. Probes associated with BMI typically have N-terminus glutamic acid (N-glutamic acid). Motif information content (bits, y-axis) is shown for each position (x-axis). (D) The N-terminus di-serine and glutamic acid motifs are present in nearly all age- and BMI-associated probes, respectively, whereas these motifs are much less common across non-age and non-BMI associated probes. Fraction of probes (y-axis) with specified motifs (color legend) are shown for age, BMI, and all other probes (x-axis). (E) The presence of N-terminus glutamic acid (E) residues is associated with BMI-correlated probes. A single E residue is comparable in significance to multiple E residues. The presence of glutamic acid at the N-terminus is significantly associated with BMI, whereas any other position in the peptide probe has limited association with BMI. (F) The di-serine score is similar across array formats. Donor samples were assayed on standard sized arrays (131 k probes, x-axis) and large-format arrays (3366 k probes y-axis) to find that the presence of N-terminus di-serine motif conferred similar association with age (axis values). Each data point represents a single donor. (G) On the 3366 k array format with both acetyl capped and uncapped probes (351 k array format, see Methods), age-associated probes are N-terminus acetylated capped. Each data point shows probe count (y-axis) for a single cutoff value to consider a probe to be age associated (x-axis). (H) Donor samples were assayed on arrays with 100% acetylated probes (x-axis) and arrays where only a fraction of probes where acetylated (y-axis). Probes that are acetylated in the split array (red) had higher association with age than those probes uncapped on the split array (black). This intra-array experimental design controls for potential inter-array confounders. Each data point represents a single probe and axes are average values across donors of specified age groups.