title: Molecular characterization and homology modeling of spermidine synthase from Synechococcus sp. PCC 7942.
abstract: Spermidine synthase (Spds) catalyzes the formation of spermidine by transferring the aminopropyl group from decarboxylated S-adenosylmethionine (dcSAM) to putrescine. The Synechococcus spds gene encoding Spds was expressed in Escherichia coli. The purified recombinant enzyme had a molecular mass of 33 kDa and showed optimal activity at pH 7.5, 37 °C. The enzyme had higher affinity for dcSAM (Km, 20 µM) than for putrescine (Km, 111 µM) and was highly specific towards the diamine putrescine with no activity observed towards longer chain diamines. The three-dimensional structural model for Synechococcus Spds revealed that most of the ligand binding residues in Spds from Synechococcus sp. PCC 7942 are identical to those of human and parasite Spds. Based on the model, the highly conserved acidic residues, Asp89, Asp159 and Asp162, are involved in the binding of substrates putrescine and dcSAM and Pro166 seems to confer substrate specificity towards putrescine.
authors.affiliation: Laboratory of Cyanobacterial Biotechnology, Department of Biochemistry, Faculty of Science, Chulalongkorn University, Bangkok, 10330, Thailand.|Structural Bioinformatics Laboratory, Biochemistry, Faculty of Science and Engineering, Åbo Akademi University, 20520, Turku, Finland.
authors.forename: Apiradee
authors.initials: A
authors.lastname: Pothipongsa
authors.affiliation: Laboratory of Cyanobacterial Biotechnology, Department of Biochemistry, Faculty of Science, Chulalongkorn University, Bangkok, 10330, Thailand.
authors.forename: Saowarath
authors.initials: S
authors.lastname: Jantaro
authors.affiliation: Structural Bioinformatics Laboratory, Biochemistry, Faculty of Science and Engineering, Åbo Akademi University, 20520, Turku, Finland.
authors.forename: Tiina A
authors.initials: TA
authors.lastname: Salminen
authors.affiliation: Laboratory of Cyanobacterial Biotechnology, Department of Biochemistry, Faculty of Science, Chulalongkorn University, Bangkok, 10330, Thailand. aran.i@chula.ac.th.
authors.forename: Aran
authors.initials: A
authors.lastname: Incharoensakdi
mesh_terms: D001216:Asparagine / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D008970:Molecular Weight; D011392:Proline / Q000378:metabolism; D011485:Protein Binding; D011700:Putrescine / Q000378:metabolism*; D012436:S-Adenosylmethionine / Q000378:metabolism*; D012689:Sequence Homology, Nucleic Acid; D011436:Spermidine Synthase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D040681:Structural Homology, Protein; D013379:Substrate Specificity; D046940:Synechococcus / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D001216:Asparagine; D012436:S-Adenosylmethionine; D011392:Proline; D011436:Spermidine Synthase; D011700:Putrescine
keywords: Homology modeling; Spermidine; Spermidine synthase; Synechococcus sp. PCC 7942