title: Crystal structures and enzymatic properties of a triamine/agmatine aminopropyltransferase from Thermus thermophilus.
abstract: To maintain functional conformations of DNA and RNA in high-temperature environments, an extremely thermophilic bacterium, Thermus thermophilus, employs a unique polyamine biosynthetic pathway and produces more than 16 types of polyamines. In the thermophile genome, only one spermidine synthase homolog (SpeE) was found and it was shown to be a key enzyme in the pathway. The catalytic assay of the purified enzyme revealed that it utilizes triamines (norspermidine and spermidine) and agmatine as acceptors in its aminopropyl transfer reaction; therefore, the enzyme was denoted as a triamine/agmatine aminopropyltransferase (TAAPT). We determined the crystal structures of the enzyme complexed with and without the aminopropyl group donor S-adenosylmethionine. Despite sequence and structural similarity with spermidine synthases from other organisms, a novel C-terminal β-sheet and differences in the catalytic site were observed. The C-terminal module interacts with the gatekeeping loop and fixes the open conformation of the loop to recognize larger polyamine substrates such as agmatine and spermidine. Additional computational docking studies suggest that the structural differences of the catalytic site also contribute to recognition of the aminopropyl/aminobutyl or guanidium moiety of the substrates of TAAPT. These results explain in part the extraordinarily diverse polyamine spectrum found in T. thermophilus.
authors: Department of Molecular Biology, Tokyo University of Pharmacy and Life Science, Tokyo 192-0392, Japan. mioohnuma@rikkyo.ac.jp
authors: Mio
authors: M
authors: Ohnuma
authors: Tadashi
authors: T
authors: Ganbe
authors: Yusuke
authors: Y
authors: Terui
authors: Masaru
authors: M
authors: Niitsu
authors: Takao
authors: T
authors: Sato
authors: Nobuo
authors: N
authors: Tanaka
authors: Masatada
authors: M
authors: Tamakoshi
authors: Keijiro
authors: K
authors: Samejima
authors: Takashi
authors: T
authors: Kumasaka
authors: Tairo
authors: T
authors: Oshima
mesh_terms: D000376:Agmatine / Q000378:metabolism; D000595:Amino Acid Sequence; D053898:Biosynthetic Pathways; D020134:Catalytic Domain; D003198:Computer Simulation; D008969:Molecular Sequence Data; D011073:Polyamines / Q000378:metabolism; D012436:S-Adenosylmethionine / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D011436:Spermidine Synthase / Q000737:chemistry*; D016963:Thermus thermophilus / Q000201:enzymology*
chemical_list: D011073:Polyamines; D000376:Agmatine; D012436:S-Adenosylmethionine; D011436:Spermidine Synthase