Abstract
Polyamines, such as putrescine, spermidine, and spermine, are polycationic mediators of cell proliferation and differentiation in most organisms. Spermidine synthase catalyzes the transfer of the aminopropyl group from decarboxylated S-adenosylmethionine to putrescine in the biosynthesis of spermidine. Here we report the crystal structure of spermidine synthase from Helicobacter pylori, which specialized in the colonization of the human stomach. Spermidine synthase from H. pylori contains 262 amino acids with a molecular weight of 30.5 kDa. Its crystal structure has been determined to 2.5Å resolution by multiwavelength anomalous dispersion (MAD) from selenomethionine (Se-Met)-containing proteins and refined to a crystallographic R-factor of 23.6% and an Rfree value of 29.5% so far. The enzyme shows the architecture of a dimer, and each monomer consists of a C-terminal domain with a Rossmann-like fold and an N-terminal beta-stranded domain. The larger C-terminal is a catalytic site and the N-terminal plays a role in maintaining the dimer structure.