LipA

LipA (PF3D7_1344600) is an apicoplast-localized lipoic acid synthase of P. falciparum, established by GFP fusion imaging of its N-terminal targeting sequence in intraerythrocytic parasites and functionally validated by complementation of E. coli lipA-deficient mutants (PMID:15225307). It is expressed at the protein level during intraerythrocytic development, with maximal abundance in early and late erythrocytic stages (PMID:15225307). Within the apicoplast, LipA acts together with LipB in de novo lipoic acid biosynthesis, generating lipoic acid from octanoyl-ACP supplied by the type II fatty acid synthesis (FAS II) pathway to furnish the cofactor for the acetyltransferase subunit of the apicoplast pyruvate dehydrogenase (PMID:22607141). Beyond this pathway placement and localization, no direct loss-of-function characterization of LipA (PF3D7_1344600) itself has been performed in the available corpus; its role in the apicoplast pathway is inferred from deletion of other FAS II and PDH components rather than from direct LipA knockout (PMID:22607141).

1. 2004 High

   It was unknown where in the parasite lipoic acid synthase acts and whether the predicted P. falciparum enzyme is a genuine lipoyl synthase; GFP targeting placed LipA in the apicoplast and bacterial complementation confirmed it is a functional lipoic acid synthase.

   Evidence GFP fusion of the N-terminal sequence for live-cell localization in P. falciparum plus complementation of an E. coli lipA-deficient mutant

   PMID:15225307

   Open questions at the time

   • N-terminal GFP fusion establishes targeting but not the localization or activity of full-length endogenous LipA
   • Complementation shows enzymatic function in a heterologous host, not in situ activity or substrate specificity in the apicoplast
   • No direct enzymatic assay of the P. falciparum protein on its native substrate
2. 2004 Medium

   Whether and when LipA protein is present during blood-stage development was unresolved; blotting showed stage-specific protein expression peaking in early and late intraerythrocytic stages.

   Evidence Northern and Western blot analyses across intraerythrocytic stages in P. falciparum

   PMID:15225307

   Open questions at the time

   • Expression timing does not establish functional requirement at any stage
   • No quantitation linking protein abundance to lipoic acid output
3. 2012 Low

   The metabolic context of LipA was unclear; synthesis of prior deletion studies placed LipA/LipB-mediated de novo lipoic acid biosynthesis exclusively in the apicoplast, drawing octanoyl-ACP from FAS II to supply the apicoplast PDH acetyltransferase.

   Evidence Review synthesis of FAS II and PDH component knockout phenotypes in Plasmodium; no direct LipA loss-of-function experiment

   PMID:22607141

   Open questions at the time

   • Pathway placement is inferred from deletion of other components, not from direct LipA/PF3D7_1344600 knockout
   • Blood-stage dispensability and inferred liver-stage requirement are not tested by targeting LipA itself
   • Physical interaction between LipA and LipB is not demonstrated

• Direct genetic and biochemical characterization of LipA (PF3D7_1344600) itself is still needed to define its native enzymatic activity, its physical partnership with LipB, and its stage-specific requirement.
• No direct LipA loss-of-function phenotype in Plasmodium
• No reconstituted enzymatic assay on octanoyl-ACP with the P. falciparum protein
• No demonstrated LipA-LipB complex or structural data