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

Chakrabarty, Subhra Prakash ; Saikumari, Yegnisettipalli Krishnaiah ; Bopanna, Monnanda P. ; Balaram, Hemalatha (2008) Biochemical characterization of plasmodium falciparum Sir2, a NAD+-dependent deacetylase Molecular and Biochemical Parasitology, 158 (2). pp. 139-151. ISSN 0166-6851

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Official URL: http://linkinghub.elsevier.com/retrieve/pii/S01666...

Related URL: http://dx.doi.org/10.1016/j.molbiopara.2007.12.003

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.

Item Type:Article
Source:Copyright of this article belongs to Elsevier Science.
Keywords:Plasmodium Falciparum Sir2; Kinetic Parameters; Rapid Equilibrium Ordered Kinetic Mechanism; Surfactin Inhibition; Subunit Association
ID Code:1258
Deposited On:04 Oct 2010 07:59
Last Modified:08 Jan 2011 03:14

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