Biochemical characterization of Plasmodium falciparum Sir2, a NAD+-dependent deacetylase

Mol Biochem Parasitol. 2008 Apr;158(2):139-51. doi: 10.1016/j.molbiopara.2007.12.003. Epub 2007 Dec 15.

Abstract

In Plasmodium falciparum, the causative agent of cerebral malaria, silent information regulator 2 (Sir2) has been implicated in pathogenesis through its role in var gene silencing. P. falciparum Sir2 (PfSir2) in addition to the catalytic core, has a 13 residue N-terminal and 4 residue C-terminal extension over the shorter Archaeoglobus fulgidus Sir2. In this paper, we highlight our studies aimed at understanding the kinetic mechanism of PfSir2 and the role of N- and C-terminal extensions in protein function and oligomerization. Bisubstrate kinetic analysis showed that PfSir2 exhibits a rapid equilibrium ordered sequential mechanism, with peptide binding preceding NAD(+). This study also reports on surfactin as a novel Sir2 inhibitor exhibiting competitive inhibition with respect to NAD(+) and uncompetitive inhibition with acetylated peptide. This inhibition pattern with surfactin provides further support for ordered binding of substrates. Surfactin was also found to be a potent inhibitor of intra-erythrocytic growth of P. falciparum with 50% inhibitory concentration in the low micromolar range. PfSir2, like the yeast homologs (yHst2 and Sir2p), is a trimer in solution. However, dissociation of trimer to monomers in the presence of NAD(+) is characteristic of the parasite enzyme. Oligomerization studies on N- and/or C-terminal deletion constructs of PfSir2 highlight the role of C-terminus of the protein in mediating homotrimerization. N-terminal deletion resulted in reduced catalytic efficiency although substrate affinity was not altered in the constructs. Interestingly, deletion of both the ends relaxed NAD(+) specificity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Dimerization
  • Enzyme Inhibitors / pharmacology
  • Kinetics
  • Lipopeptides
  • Molecular Sequence Data
  • NAD / metabolism*
  • Peptides, Cyclic / pharmacology
  • Plasmodium falciparum / enzymology*
  • Plasmodium falciparum / genetics
  • Plasmodium falciparum / growth & development
  • Protein Subunits / metabolism
  • Protozoan Proteins / antagonists & inhibitors
  • Protozoan Proteins / chemistry
  • Protozoan Proteins / genetics
  • Protozoan Proteins / metabolism
  • Sequence Alignment
  • Sirtuins / antagonists & inhibitors
  • Sirtuins / chemistry
  • Sirtuins / genetics
  • Sirtuins / metabolism*

Substances

  • Enzyme Inhibitors
  • Lipopeptides
  • Peptides, Cyclic
  • Protein Subunits
  • Protozoan Proteins
  • NAD
  • surfactin peptide
  • Sirtuins