To ensure that the structures obtained are significant for the study and represent a peptide and not a protein sequence motif, the PDB structures whose sequence had a difference in length greater than five residues compared to the GRAMPA sequences were eliminated. Subsequently, to guarantee a close relationship between the GRAMPA sequences and the PDB sequences, we calculated the Smith-Waterman distance 56 between both groups. This algorithm performs a local alignment of biological sequences to search for similar regions between them, comparing motifs of different sizes to identify conserved domains, so it is more reliable than the percentage identity provided by the PDBe REST API sequence search module. The Smith-Waterman distance was calculated as a percentage for each GRAMPA peptide sequence-PDB structure pair, and only those pairs with a Smith-Waterman distance of at least 0.70 (1 indicates two identical sequences) were retained. Finally, due to the limitations of the secondary structure prediction algorithms we use below, we removed sequences longer than 50 residues. ). We used the PDBe REST API secondary structure module, which details the ranges of ordinary secondary structures (H: helices, E: extended strand/β-sheets and C: coils) of residues found in a polypeptide chain to determine the secondary structure of the experimental tridimensional structures reported in PDBe. Some sequences in PDBe have more than one reported structure, which may be because they were reported by different research laboratories, were obtained by different experimental methods, or under different conditions. Because some of these structures show discrepancies in the secondary structure ranges, we kept only those sequences with only one reported structure. Secondary structure ranges (H, E, C) were converted in percentages (%).