8.A.212.  The d-Amino Acid Peptidase (dAAP) Family 

Bacteria assemble a non-toxic precursor on an N-acyl-d-asparagine prodrug motif in the cytoplasm, then export it to the periplasm where a dedicated d-amino peptidase hydrolyzes the prodrug motif. These prodrug-activating peptidases contain N-terminal periplasmic S12 hydrolase domains and C-terminal transmembrane domains (TMDs) of varying lengths: type I peptidases contain three transmembrane helices, and type II peptidases have an additional C-terminal ABC half-transporter. Studies have addressed the role of the TMSs in function, substrate specificity, and the biological assembly of ClbP (see TC# 1.C.74), the type I peptidase that activates colibactin. Velilla et al. 2023 used modeling and sequence analyses to extend these observations to other prodrug-activating peptidases and ClbP-like proteins which are not part of prodrug resistance gene clusters. These ClbP-like proteins may play roles in the biosynthesis or degradation of other natural products, including antibiotics, may adopt different TM folds, and have different substrate specificities compared to prodrug-activating homologs. ClbP may also interact with transporters in the cell, and this association may be important for the export of other natural products.