Enzymatic alpha-amidation system in scorpion venom glands. Enzymatic alpha-amidation system in scorpion venom glands

Abstract: C-Terminal amidation is one of the most commonly found posttranslational modification in peptides of the scorpion venoms. It is paramount for the correct biological function of ion channel-acting toxins and antimicrobial peptides, among others. The discovery of canonical amidation sequences in transcriptome-derived scorpion proproteins suggests that a conserved alpha-amidation enzymatic system must be responsible for this modification in scorpions. A transcriptomic approach was employed to identify the sequences putatively coding for enzymes of the alpha-amidation pathway. A dual enzymatic alpha-amidation system was found, consisting, on one side, of the membrane-anchored bifunctional peptidylglycine alpha-amidating monooxygenase (PAM) and of the paralogue soluble monofunctional peptidylglycine alpha-hydroxylating monooxygenase (PHMm) and peptidyl-alpha-hydroxyglycine alpha-amidating lyase (PALm), on the other. Independent genes code for these three enzymes. The amino acid residues responsible for ion coordination and enzymatic activity are conserved in these sequences, suggesting that the enzymes are functional. The presence of potential endoproteolytic recognition sites for proprotein convertases in the PAM sequence indicates that PAM-derived soluble isoforms can also be expressed. Sequences potentially coding for proprotein convertases (PC1 and PC2) and carboxypeptidase E (CPE), other enzymes of the alpha-amidation pathway, were also found, confirming the presence of this pathway in scorpions.