The Amino Acid Composition (AAC) is the fraction of each amino acid type within a peptide sequence of length N. The fractions f of all 20 natural amino acids r (r = 1, 2, ..., 20) were calculated using the equation (Eq.4); they were looped over all M sequences in a given dataset and averaged out. The AAC values were measured using R package protr (v.1.0-1) . The results for ACP-S and ACP-NS datasets are summarized in Table .