Molecular characterization and homology modeling of spermidine synthase from Synechococcus sp. PCC 7942
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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 (K m, 20 µM) than for putrescine (K m, 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.
KeywordsSpermidine synthase Spermidine Synechococcus sp. PCC 7942 Homology modeling
Apiradee Pothipongsa thanks the Commission on Higher Education, Thailand under Science Achievement Scholarship, the 90th Anniversary of Chulalongkorn University (CU) Fund, the EXPERTS Erasmus Mundus scholarship for financial support. We thank Prof. Keijiro Samejima for providing dcSAM. Aran Incharoensakdi thanks CU Food and Water Cluster (CU-58-011-FW) and Thailand Research Fund (IRG5780008) for financial support. Tiina A. Salminen thanks Sigrid Juselius Foundation for financial support. Use of Biocenter Finland infrastructure at Åbo Akademi University (bioinformatics, structural biology, and translational activities) is acknowledged.
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Conflict of interest
The authors declare no conflict of interest.
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