MCAT

MCAT (PF3D7_1312000) is the malonyl-CoA:ACP transacylase that initiates apicoplast type II fatty acid biosynthesis in malaria parasites (PMID:12549938). Recombinant P. falciparum MCAT transfers a malonyl group from malonyl-CoA to the acyl carrier protein pfACP in vitro, and the resulting malonyl-pfACP is a direct substrate for pfKASIII, placing MCAT immediately upstream of the KASIII-catalyzed condensation step in the pathway (PMID:12549938). Substrate recognition depends on the mature form of pfACP: pfACP bearing its N-terminal apicoplast transit peptide is not accepted, indicating the transit peptide interferes with malonyl transfer (PMID:12549938). Genetic disruption in the rodent malaria parasite P. berghei defines MCAT's physiological role as stage-specific—it is dispensable for asexual blood-stage and mosquito-stage propagation but essential for late liver-stage development, where MCAT-null hepatic parasites show impaired apicoplast biogenesis and nuclear division and fail to form hepatic merozoites (PMID:40379677). Beyond this catalytic and life-cycle characterization, no structural or regulatory detail for MCAT has been established in the available corpus.

1. 2003 High

   Establishing whether PF3D7_1312000 was a functional malonyl-CoA:ACP transacylase settled the identity of the enzyme initiating parasite type II fatty acid synthesis.

   Evidence In vitro biochemical assay with purified recombinant pfMCAT and pfACP

   PMID:12549938

   Open questions at the time

   • Catalytic residues and structural basis of malonyl transfer not defined
   • Kinetic parameters and regulation not characterized
2. 2003 Medium

   Testing transit-peptide-bearing pfACP versus mature pfACP addressed which form of the carrier protein MCAT recognizes, revealing that the apicoplast transit peptide blocks catalysis.

   Evidence In vitro enzymatic assay comparing pfACP and pfACP(trans) as MCAT substrates

   PMID:12549938

   Open questions at the time

   • Single in vitro negative result
   • Structural basis of the transit-peptide interference not resolved
   • Physiological relevance of the unprocessed form unclear
3. 2003 High

   Feeding the malonyl-pfACP product into a pfKASIII reaction placed MCAT within the ordered initiation pathway, linking its output to downstream condensation.

   Evidence Sequential in vitro enzymatic assay: MCAT-generated malonyl-pfACP used as substrate for pfKASIII

   PMID:12549938

   Open questions at the time

   • In vitro reconstitution only; in vivo flux through this route not measured
   • Full downstream elongation cascade not tested in the same system
4. 2025 Medium

   Genetic knockout across the life cycle answered where MCAT is physiologically required, demonstrating a specific essential role in late liver-stage development rather than in blood or mosquito stages.

   Evidence MCAT knockout in rodent malaria parasites with phenotypic analysis of apicoplast biogenesis, nuclear division, and merozoite formation across life-cycle stages

   PMID:40379677

   Open questions at the time

   • Single lab; not confirmed in P. falciparum
   • Mechanistic link between loss of fatty acid synthesis and the apicoplast/nuclear-division defect not resolved
   • Whether the defect is due solely to loss of transacylase activity not tested by catalytic-dead complementation

• How MCAT activity is regulated and how its loss mechanistically couples to apicoplast biogenesis and nuclear division in hepatic parasites remains unresolved.
• No structural model of MCAT
• No catalytic-dead rescue linking enzymatic activity to the liver-stage phenotype
• P. falciparum knockout phenotype not established