Sulfur mobilization for Fe-S cluster assembly by the essential SUF pathway in the Plasmodium falciparum apicoplast and its inhibition.
The plastid of the malaria parasite, the apicoplast, is essential for parasite survival. It houses several pathways of bacterial origin that are considered attractive sites for drug intervention. Among these is the sulfur mobilization (SUF) pathway of Fe-S cluster biogenesis. Although the SUF pathway is essential for apicoplast maintenance and parasite survival, there has been limited biochemical investigation of its components and inhibitors of Plasmodium SUFs have not been identified. We report the characterization of two proteins, Plasmodium falciparum SufS (PfSufS) and PfSufE, that mobilize sulfur in the first step of Fe-S cluster assembly and confirm their exclusive localization to the apicoplast. The cysteine desulfurase activity of PfSufS is greatly enhanced by PfSufE, and the PfSufS-PfSufE complex is detected in vivo. Structural modeling of the complex reveals proximal positioning of conserved cysteine residues of the two proteins that would allow sulfide transfer from the PLP (pyridoxal phosphate) cofactor-bound active site of PfSufS. Sulfide release from the l-cysteine substrate catalyzed by PfSufS is inhibited by the PLP inhibitor d-cycloserine, which forms an adduct with PfSufS-bound PLP. d-Cycloserine is also inimical to parasite growth, with a 50% inhibitory concentration close to that reported for Mycobacterium tuberculosis, against which the drug is in clinical use. Our results establish the function of two proteins that mediate sulfur mobilization, the first step in the apicoplast SUF pathway, and provide a rationale for drug design based on inactivation of the PLP cofactor of PfSufS.
Division of Molecular and Structural Biology, CSIR-Central Drug Research Institute, Lucknow, India.
Manish
M
Charan
Division of Molecular and Structural Biology, CSIR-Central Drug Research Institute, Lucknow, India.
Nidhi
N
Singh
Division of Molecular and Structural Biology, CSIR-Central Drug Research Institute, Lucknow, India.
Bijay
B
Kumar
Division of Parasitology, CSIR-Central Drug Research Institute, Lucknow, India.
Kumkum
K
Srivastava
Division of Molecular and Structural Biology, CSIR-Central Drug Research Institute, Lucknow, India.
Mohammad Imran
MI
Siddiqi
Division of Molecular and Structural Biology, CSIR-Central Drug Research Institute, Lucknow, India saman.habib@gmail.com.
Saman
S
Habib
D000963:Antimetabolites / Q000494:pharmacology; D063546:Apicoplasts / Q000378:metabolism*; D013437:Carbon-Sulfur Lyases / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D003523:Cycloserine / Q000494:pharmacology; D003545:Cysteine / Q000378:metabolism; D020128:Inhibitory Concentration 50; D007506:Iron-Sulfur Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D008961:Models, Structural; D016296:Mutagenesis; D010963:Plasmodium falciparum / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D025941:Protein Interaction Mapping; D015800:Protozoan Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism; D011732:Pyridoxal Phosphate / Q000378:metabolism; D013440:Sulfides / Q000378:metabolism; D013455:Sulfur / Q000378:metabolism*
D000963:Antimetabolites; D007506:Iron-Sulfur Proteins; D015800:Protozoan Proteins; D013440:Sulfides; D011732:Pyridoxal Phosphate; D013455:Sulfur; D003523:Cycloserine; D013437:Carbon-Sulfur Lyases; C080546:cysteine desulfurase; D003545:Cysteine