The Suf Iron-Sulfur Cluster Synthesis Pathway Is Required for Apicoplast Maintenance in Malaria Parasites

Abstract

The apicoplast organelle of the malaria parasite Plasmodium falciparum contains metabolic pathways critical for liver-stage and blood-stage development. During the blood stages, parasites lacking an apicoplast can grow in the presence of isopentenyl pyrophosphate (IPP), demonstrating that isoprenoids are the only metabolites produced in the apicoplast which are needed outside of the organelle. Two of the isoprenoid biosynthesis enzymes are predicted to rely on iron-sulfur (FeS) cluster cofactors, however, little is known about FeS cluster synthesis in the parasite or the roles that FeS cluster proteins play in parasite biology. We investigated two putative FeS cluster synthesis pathways (Isc and Suf) focusing on the initial step of sulfur acquisition. In other eukaryotes, these proteins can be located in multiple subcellular compartments, raising the possibility of cross-talk between the pathways or redundant functions. In P. falciparum, SufS and its partner SufE were found exclusively the apicoplast and SufS was shown to have cysteine desulfurase activity in a complementation assay. IscS and its effector Isd11 were solely mitochondrial, suggesting that the Isc pathway cannot contribute to apicoplast FeS cluster synthesis. The Suf pathway was disrupted with a dominant negative mutant resulting in parasites that were only viable when supplemented with IPP. These parasites lacked the apicoplast organelle and its organellar genome – a phenotype not observed when isoprenoid biosynthesis was specifically inhibited with fosmidomycin. Taken together, these results demonstrate that the Suf pathway is essential for parasite survival and has a fundamental role in maintaining the apicoplast organelle in addition to any role in isoprenoid biosynthesis.

Sulfur Mobilization for Fe-S Cluster Assembly by the Essential SUF Pathway in the Plasmodium falciparum Apicoplast and Its Inhibition

“…The antimalarial effect of inhibition of Fe-S assembly on target proteins in the apicoplast has been recently demonstrated through the generation of dominant negative SufC mutant parasites (7). These parasites lost the apicoplast and the organellar genome and were viable only when supplemented with isopentenyl pyrophosphate, an essential product of the apicoplast DOXP pathway that supports parasite survival in blood culture even when the apicoplast is lost (46).…”

“…It harbors unique pathways such as the type II fatty acid biosynthesis pathway, the DOXP pathway of isoprenoid synthesis, and the heme biosynthesis pathway (3)(4)(5), that offer potential novel sites for drug intervention at different stages of the infection cycle. In addition, experimental evidence of the existence of the sulfur mobilization (SUF) pathway for biogenesis of Fe-S clusters on organellar proteins was provided by our laboratory (6), and this pathway has recently been shown to be essential for apicoplast maintenance in erythrocytic stages of Plasmodium falciparum (7).…”

“…encode the ISC and SUF pathways (8,17), some of whose constituent proteins have recently been shown to partition to the parasite mitochondrion and apicoplast, respectively (6,7). The 35-kb genome of the apicoplast carries the gene encoding SufB, while all of the other proteins of the SUF pathway are encoded by the nucleus.…”

“…The 35-kb genome of the apicoplast carries the gene encoding SufB, while all of the other proteins of the SUF pathway are encoded by the nucleus. In P. falciparum, the targeting of SufC, SufS, and SufE to the apicoplast and the interaction of apicoplastencoded SufB with SufC have been demonstrated (6,7). Nucleusencoded SufA and SufD homologues carrying apicoplast-targeting signal and transit peptide sequences have been identified in P. falciparum (6,17).…”

Functional Dynamics Revealed by the Structure of the SufBCD Complex, a Novel ATP-binding Cassette (ABC) Protein That Serves as a Scaffold for Iron-Sulfur Cluster Biogenesis

“…Structural and mechanistic understanding of Suf systems may enable the development of new antibiotics that target the SufBCD complex. Indeed, a recent study demonstrated that the Suf system of malaria parasites is essential for survival and plays a fundamental role in maintaining the apicoplast organelle (58). In eukaryotes, including mammalian cells, the ISC system (59) and its dependent CIA system (60) are responsible for nascent Fe-S cluster biogenesis.…”