Studies on active site mutants of P-falciparum adenylosuccinate synthetase: Insights into enzyme catalysis and activation

Mehrotra, Sonali and Mylarappa, BN and Iyengar, Prathima and Balaram, Hemalatha (2010) Studies on active site mutants of P-falciparum adenylosuccinate synthetase: Insights into enzyme catalysis and activation. In: Biochimica et Biophysica Acta (BBA) - Proteins & Proteomics, 1804 (10). pp. 1996-2002.

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Abstract

Adenylosuccinate synthetase catalyzes a reversible reaction utilizing IMP, GTP and aspartate in the presence of Mg2+ to form adenylosuccinate, GDP and inorganic phosphate. Comparison of similarly liganded complexes of Plasmodium falciparum, mouse and Escherichia coil AdSS reveals H-bonding interactions involving nonconserved catalytic loop residues (Asn429, Lys62 and Thr307) that are unique to the parasite enzyme. Site-directed mutagenesis has been used to examine the role of these interactions in catalysis and structural organization of P. falciparum adenylosuccinate synthetase (PfAdSS). Mutation of Asn429 to Val, Lys62 to Leu and Thr307 to Val resulted in an increase in K-m values for IMP, GTP and aspartate, respectively along with a 5 fold drop in the k(cat) value for N429V mutant suggesting the role of these residues in ligand binding and/or catalysis. We have earlier shown that the glycolytic intermediate, fructose 1,6 bisphosphate, which is an inhibitor of mammalian AdSS is an activator of the parasite enzyme. Enzyme kinetics along with molecular docking suggests a mechanism for activation wherein F16BP seems to be binding to the Asp loop and inducing a conformation that facilitates aspartate binding to the enzyme active site. Like in other AdSS, a conserved arginine residue (Arg155) is involved in dimer crosstalk and interacts with IMP in the active site of the symmetry related subunit of PfAdSS. We also report on the iochemical characterization of the arginine mutants (R155L, R155K and R155A) which suggests that unlike in E. coil AdSS, Arg155 in PfAdSS influences both ligand binding and catalysis. (C) 2010 Elsevier B.V. All rights reserved.

Item Type:	Journal Article
Publication:	Biochimica et Biophysica Acta (BBA) - Proteins & Proteomics
Publisher:	Elsevier Science
Additional Information:	Copyright of this article belongs to Elsevier Science.
Keywords:	P.falciparum; Adenylosuccinate synthetase; Site-directed mutagenesis; Fructose 1,6 bisphosphate; Docking.
Department/Centre:	Division of Biological Sciences > Molecular Biophysics Unit
Date Deposited:	04 Oct 2010 08:16
Last Modified:	04 Oct 2010 08:16
URI:	http://eprints.iisc.ac.in/id/eprint/32940

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