# $\delta$-Aminolevulinic Acid Dehydratase from Plasmodium falciparum

Dhanasekaran, Shanmugham and Chandra, Nagasuma R and Sagar, Chandrasekhar BK and Rangarajan, Pundi N and Padmanaban, Govindarajan (2004) $\delta$-Aminolevulinic Acid Dehydratase from Plasmodium falciparum. In: Journal of Biological Chemistry, 279 (8). pp. 6934-6942.

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## Abstract

The heme biosynthetic pathway of the malaria parasite is a drug target and the import of host $\delta$-aminolevulinate dehydratase (ALAD), the second enzyme of the pathway, from the red cell cytoplasm by the intra erythrocytic malaria parasite has been demonstrated earlier in this laboratory. In this study, ALAD encoded by the Plasmodium falciparum genome (PfALAD) has been cloned, the protein overexpressed in Escherichia coli, and then characterized. The mature recombinant enzyme (rPfALAD) is enzymatically active and behaves as an octamer with a subunit $M_r$ of 46,000. The enzyme has an alkaline pH optimum of 8.0 to 9.0. rPfALAD does not require any metal ion for activity, although it is stimulated by 20–30% upon addition of $Mg^{2+}.$ The enzyme is inhibited by $Zn^{2+}$ and succinylacetone. The presence of PfALAD in P. falciparum can be demonstrated by Western blot analysis and immunoelectron microscopy. The enzyme has been localized to the apicoplast of the malaria parasite. Homology modeling studies reveal that PfALAD is very similar to the enzyme species from Pseudomonas aeruginosa, but manifests features that are unique and different from plant ALADs as well as from those of the bacterium. It is concluded that PfALAD, while resembling plant ALADs in terms of its alkaline pH optimum and apicoplast localization, differs in its $Mg^{2+}$ independence for catalytic activity or octamer stabilization. Expression levels of PfALAD in P. falciparum, based on Western blot analysis, immunoelectron microscopy, and EDTA-resistant enzyme activity assay reveals that it may account for about 10% of the total ALAD activity in the parasite, the rest being accounted for by the host enzyme imported by the parasite. It is proposed that the role of PfALAD may be confined to heme synthesis in the apicoplast that may not account for the total de novo heme biosynthesis in the parasite.

Item Type: Journal Article The copyright belongs to American Society for Biochemistry and Molecular Biology. Division of Information Sciences > BioInformatics CentreDivision of Biological Sciences > Biochemistry 26 Feb 2007 19 Sep 2010 04:27 http://eprints.iisc.ernet.in/id/eprint/7054