NFS1

NFS1 (PF3D7_0727200) is the mitochondrial cysteine desulfurase that constitutes the catalytic core of the iron-sulfur cluster (ISC) biosynthesis machinery in Plasmodium falciparum, localizing exclusively to the mitochondrion and therefore not contributing to apicoplast Fe-S cluster synthesis, which relies on the separate Suf pathway (PMID:24086138). NFS1 assembles with the effector protein PfIsd11 and the scaffold PfIscU into an unusual symmetric hetero-hexamer built around an NFS1 tetramer (2×(2PfIscS–2PfIsd11–2PfIscU)), in contrast to the canonical dimeric desulfurase seen in bacteria, yeast, and humans (PMID:34032321). Within this complex NFS1 supplies sulfur for de novo Fe-S cluster assembly, and PfIscU directly generates [4Fe-4S] clusters and transfers them to apo-aconitase B without passing through a [2Fe-2S] intermediate, bypassing a conversion step required in other organisms (PMID:34032321). The stability of the NFS1–Isd11 complex depends on physical interaction with the divergent mitochondrial acyl carrier protein (mACP), which binds and stabilizes NFS1 despite lacking the 4-phosphopantetheine group that mediates this interaction elsewhere; mACP knockdown depletes NFS1 protein and the Rieske Fe-S subunit of electron transport chain complex III, coupling NFS1-dependent Fe-S biogenesis to mitochondrial respiratory integrity (PMID:34612205).

1. 2013 Medium

   Establishing where NFS1 acts was the first step in defining its pathway role, since Plasmodium compartmentalizes Fe-S synthesis between mitochondrion and apicoplast; localizing NFS1 to the mitochondrion assigned it exclusively to the ISC pathway.

   Evidence subcellular localization/complementation experiments in P. falciparum

   PMID:24086138

   Open questions at the time

   • Does not establish the catalytic activity or complex composition of NFS1
   • Does not identify downstream Fe-S recipient proteins
2. 2021 High

   The architecture of the desulfurase machine was unknown; reconstitution and SAXS revealed that NFS1 assembles into a tetramer-based hetero-hexamer with Isd11 and IscU, distinguishing the parasite complex from the canonical dimeric form.

   Evidence biochemical complex reconstitution, SAXS, and spectral studies in P. falciparum

   PMID:34032321

   Open questions at the time

   • No atomic-resolution structure of the hexamer
   • Functional consequence of the tetrameric versus dimeric arrangement not tested
3. 2021 High

   Whether the parasite follows the canonical stepwise Fe-S assembly route was open; in vitro assays showed the NFS1-containing complex enables direct [4Fe-4S] assembly and transfer to apo-aconitase B, bypassing a [2Fe-2S] intermediate.

   Evidence in vitro Fe-S cluster assembly and cluster transfer assays to apo-aconitase B

   PMID:34032321

   Open questions at the time

   • Full range of physiological Fe-S recipient proteins not defined
   • Mechanism of direct [4Fe-4S] formation not resolved structurally
4. 2021 High

   The determinants of NFS1 stability and its link to mitochondrial function were unclear; mACP was shown to bind and stabilize the Isd11–NFS1 complex in a phosphopantetheine-independent manner, with its depletion causing loss of NFS1 and the Rieske Fe-S protein.

   Evidence co-purification binding studies and ligand-dependent mACP knockdown with proteomic readout in P. falciparum

   PMID:34612205

   Open questions at the time

   • Structural basis of Ppant-independent mACP binding to NFS1 not defined
   • Whether mACP regulates NFS1 catalytic activity beyond stabilizing its abundance is untested

• The full spectrum of NFS1-dependent Fe-S apoprotein clients, the regulation of desulfurase activity in vivo, and a high-resolution structure of the tetrameric complex remain to be established.
• No atomic structure of the NFS1 hetero-hexamer
• In vivo essentiality and phenotype of NFS1 depletion not directly reported in this corpus
• Complete Fe-S client repertoire beyond aconitase B and the Rieske protein unknown