Abstract
Spermidine synthase (putrescine aminopropyltransferase, PAPT) catalyzes the transfer of the aminopropyl group from decarboxylated S-adenosylmethionine (dcAdoMet) to putrescine in the biosynthesis of spermidine. PAPT of Helicobacter pylori (HpPAPT) is encoded by the speE gene. HpPAPT shares low sequence homology with other PAPTs and lacks their significant sequences. The three-dimensional structure of HpPAPT has been determined by multiwavelength anomalous dispersion (MAD) in this study. HpPAPT comprises an N-terminal □-stranded domain and a C-terminal Rossmann-like domain, with a binding pocket between the two domains. Comparing with other PAPTs, HpPAPT has a putative active site with a bigger space, a different electrostatic potential surface of less acidity, and numerous unconserved residues. Due to the lack of a gatekeeping loop, HpPAPT may need to implement a significant conformational change to accommodate the ligand binding. In addition, because HpPAPT contains the characteristic sequence as well as the unique conformation and PAPTs are essential for bacterial cell viability, HpPAPT can be a potential drug target for H. pylori.