FeSOD

PF3D7_0814900 (FeSOD) is an iron-dependent superoxide dismutase of Plasmodium falciparum that contributes to the intraerythrocytic parasite's antioxidant defence (PMID:8920001). Biochemically it belongs to the Fe-SOD class: its activity is cyanide-resistant and hydrogen-peroxide-sensitive, and it was purified and cloned as a subunit whose phylogeny groups with typical protozoan and bacterial Fe-SODs (PMID:8920001). The functional enzyme is a homodimer carrying roughly 1.7 Fe equivalents per dimer, and its 2.5 Å crystal structure shows a two-domain fold with an iron centre coordinated by three histidines, one aspartate, and a solvent molecule, plus a hydrogen-bonding lattice linking the two active centres; the dimer interface diverges from human MnSOD, defining a basis for parasite-selective inhibitor design (PMID:11897129, PMID:17020617). EPR resolves two distinct high-spin Fe environments, and mutagenesis established that W71 is not a primary determinant of H2O2 sensitivity (PMID:11897129). FeSOD is cytosolic in intraerythrocytic stages, its mRNA is far more abundant than that of the second parasite SOD gene, and both are up-regulated by oxidative stress (PMID:15279958). Beyond this enzymatic and structural characterization, the corpus places FeSOD in a multi-protein complex with PfDegP, PfHsp70, and enolase (PMID:24494818); no functional role for FeSOD within that complex has been characterized in the available corpus.

1. 1996 High

   Establishing which SOD class the P. falciparum enzyme belongs to was needed to define the parasite's superoxide-scavenging chemistry; purification and inhibitor profiling identified it as a genuine iron-dependent SOD distinct from Cu/Zn enzymes.

   Evidence enzyme purification, N-terminal sequencing, cDNA cloning, phylogenetic analysis, and activity assays with inhibitors in P. falciparum

   PMID:8920001

   Open questions at the time

   • Does not establish subcellular localization or in vivo contribution to parasite survival
   • Catalytic mechanism not resolved at residue level
2. 2002 High

   The oligomeric state, metal stoichiometry, and the residue basis of H2O2 sensitivity were unknown; recombinant characterization showed a homodimer with ~1.7 Fe per dimer, two distinct Fe environments, and ruled out W71 as the primary H2O2-sensitivity determinant.

   Evidence recombinant expression in SOD-deficient E. coli, EPR spectroscopy, W71V site-directed mutagenesis, activity assays, and molecular modelling

   PMID:11897129

   Open questions at the time

   • The actual structural determinant of H2O2 sensitivity remains unidentified
   • Functional meaning of the two distinct Fe EPR environments not resolved
3. 2004 Medium

   Whether FeSOD acts in the cytosol and how it is expressed relative to the second parasite SOD was unresolved; localization and expression analysis placed it in the cytosol with predominant and stress-inducible mRNA expression.

   Evidence immunofluorescence microscopy and Northern blot analysis in P. falciparum intraerythrocytic stages

   PMID:15279958

   Open questions at the time

   • mRNA abundance does not establish relative protein-level contribution
   • Does not test whether FeSOD is required for oxidative-stress survival
4. 2006 High

   A high-resolution structural model was needed to define the active site and to enable selective drug design; the crystal structure revealed the iron coordination geometry and a dimer interface distinct from human MnSOD.

   Evidence recombinant expression, X-ray crystallography at 2.5 Å by molecular replacement, and analytical ultracentrifugation in P. falciparum

   PMID:17020617

   Open questions at the time

   • No inhibitor-bound structure or validated selective inhibitor reported
   • Catalytic cycle not directly captured
5. 2014 Low

   Whether FeSOD functions in isolation or within a protein assembly was open; interaction analysis placed FeSOD in a complex with PfDegP, PfHsp70, and enolase.

   Evidence anti-bait co-immunoprecipitation and surface plasmon resonance in P. falciparum

   PMID:24494818

   Open questions at the time

   • Single co-IP/SPR study without reciprocal validation or knockdown
   • No functional role for FeSOD within the complex demonstrated
   • Stoichiometry and physiological trigger of complex formation unknown

• The in vivo requirement of FeSOD for parasite antioxidant defence and survival, and its functional role within the PfDegP/PfHsp70/enolase complex, remain to be established.
• No genetic knockout/knockdown phenotype in the corpus
• No validated selective inhibitor despite structural rationale
• Functional consequence of complex membership uncharacterized