Figure 3. Observed amino acid frequency and predicted solvent molecular surface exposure of amino acids.

(a) Four amino acids (Arg, His, Ile, Pro) were significantly more or less expressed in the pellicle (white) than in the saliva (grey). (b) Mean fold-changes (log2) of amino acid expression in the pellicle compared with saliva. Proteins of the pellicle included Gln, Gly, Tyr, Asn, Cys and Phe more often than salivary proteins, whereas expression frequency of all other amino acids was lower in pellicle than salivary proteins. (c) Summary of predicted amino acid exposure in proteins of the pellicle (white) and the saliva (grey). A significant difference was found for Asp only. (d) Predicted exposure of amino acids was higher in the pellicle than salivary proteins for all but five amino acids (Ser, Glu, Ala, Val, Leu). (e) Combined results (mean ± 95% CI [log2]) did not reveal a single amino acid which was both differently expressed and differently exposed. Mann-Whitney-U test was applied for statistical comparison: *p < 0.01, **p < 0.001, ***p < 0.0001; aa  =  amino acid.