Scorpion venom non-disulfide-bridged peptides (NDBP)

Scorpion venom non-disulfide-bridged peptides (NDBPs) represent a highly divergent and versatile group of peptides in regards to their primary sequence, rending them difficult to classify. Zeng et al. first established a classification system in 2005 using the criteria of pharmacological activity, peptide length and sequence similarity. At that time, there were only 17 peptides that were classified in six subfamilies with the suggestion that each peptide should be named NDBP-x.y where x and y stand for the subfamily and peptide number within the subfamily, which should be assigned chronologically. Due to the significant increase in the number of NDBPs discovered in the last decade, this classification system was updated in 2014 by Almaayatah and Albalas (Table 1). This new classification system uses the same criteria devised by Zeng and colleagues, slightly changes the previous classification (from 6 to 5 families) and only takes characterized peptides into consideration. As many uncharacterized peptides exist and need to be classified in a family, they have been classified in UniProtKB/Swiss-Prot as belonging to the respective family and are available through the "All peptides" rows of Table 1. Note that group 5 proposed by Almaayatah and Albalas describes "antimalarial peptides" whose function in the venom is surely different. We decided to keep this function in the table in order to respect the pharmacological activity criteria. However, note that uncharacterized peptides of 24-29 residues (that can be classified as medium-length antimicrobial peptides or as antimalarial peptides) are only classified in UniProtKB/Swiss-Prot as "medium-length antimicrobial peptides" because the aim of scorpion venom is not to fight plasmodia.