A Novel polyamine allosteric site of speg from vibrio cholerae is revealed by its dodecameric structure

Ekaterina V. Filippova, Misty L. Kuhn, Jerzy Osipiuk, Olga Kiryukhina, Andrzej Joachimiak, Miguel A. Ballicora, Wayne F. Anderson*

*Corresponding author for this work

Research output: Contribution to journalArticle

16 Scopus citations

Abstract

Spermidine N-acetyltransferase, encoded by the gene speG, catalyzes the initial step in the degradation of polyamines and is a critical enzyme for determining the polyamine concentrations in bacteria. In Escherichia coli, studies have shown that SpeG is the enzyme responsible for acetylating spermidine under stress conditions and for preventing spermidine toxicity. Not all bacteria contain speG, and many bacterial pathogens have developed strategies to either acquire or silence it for pathogenesis. Here, we present thorough kinetic analyses combined with structural characterization of the VCA0947 SpeG enzyme from the important human pathogen Vibrio cholerae. Our studies revealed the unexpected presence of a previously unknown allosteric site and an unusual dodecameric structure for a member of the Gcn5-related N-acetyltransferase superfamily. We show that SpeG forms dodecamers in solution and in crystals and describe its three-dimensional structure in several ligand-free and liganded structures. Importantly, these structural data define the first view of a polyamine bound in an allosteric site of an N-acetyltransferase. Kinetic characterization of SpeG from V. cholerae showed that it acetylates spermidine and spermine. The behavior of this enzyme is complex and exhibits sigmoidal curves and substrate inhibition. We performed a detailed non-linear regression kinetic analysis to simultaneously fit families of substrate saturation curves to uncover a simple kinetic mechanism that explains the apparent complexity of this enzyme. Our results provide a fundamental understanding of the bacterial SpeG enzyme, which will be key toward understanding the regulation of polyamine levels in bacteria during pathogenesis.

Original languageEnglish (US)
Pages (from-to)1316-1334
Number of pages19
JournalJournal of Molecular Biology
Volume427
Issue number6
DOIs
StatePublished - Mar 27 2015

Keywords

  • GNAT
  • acetyltransferase
  • allosteric enzyme
  • dodecamer
  • spermidine/spermine

ASJC Scopus subject areas

  • Structural Biology
  • Molecular Biology

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