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J Struct Biol. 2010 Mar;169(3):277-85. doi: 10.1016/j.jsb.2009.12.024. Epub 2010 Jan 4.

The crystal structure of Escherichia coli spermidine synthase SpeE reveals a unique substrate-binding pocket.

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Department of Biological Sciences, 14 Science Drive 4, National University of Singapore, Singapore 117543, Republic of Singapore.


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.

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