title: The crystal structure of Escherichia coli spermidine synthase SpeE reveals a unique substrate-binding pocket.
abstract: Polyamines are essential in all branches of life. Biosynthesis of spermidine, one of the most ubiquitous polyamines, is catalyzed by spermidine synthase (SpeE). Although the function of this enzyme from Escherichia coli has been thoroughly characterised, its structural details remain unknown. Here, we report the crystal structure of E. coli SpeE and study its interaction with the ligands by isothermal titration calorimetry and computational modelling. SpeE consists of two domains - a small N-terminal beta-strand domain, and a C-terminal catalytic domain that adopts a canonical methyltransferase (MTase) Rossmann fold. The protein forms a dimer in the crystal and in solution. Structural comparison of E. coli SpeE to its homologs reveals that it has a large and unique substrate-binding cleft that may account for its lower amine substrate specificity.
authors.affiliation: Department of Biological Sciences, 14 Science Drive 4, National University of Singapore, Singapore 117543, Republic of Singapore.
authors.forename: Xingding
authors.initials: X
authors.lastname: Zhou
authors.forename: Teck Khiang
authors.initials: TK
authors.lastname: Chua
authors.forename: Karolina L
authors.initials: KL
authors.lastname: Tkaczuk
authors.forename: Janusz M
authors.initials: JM
authors.lastname: Bujnicki
authors.forename: J
authors.initials: J
authors.lastname: Sivaraman
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites / Q000235:genetics / Q000502:physiology; D002151:Calorimetry; D020134:Catalytic Domain / Q000235:genetics / Q000502:physiology; D018360:Crystallography, X-Ray / Q000379:methods*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D055503:Protein Multimerization; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D011436:Spermidine Synthase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D029968:Escherichia coli Proteins; D011436:Spermidine Synthase