COX1

PF3D7_MIT02100 (COX1) encodes cytochrome c oxidase subunit 1, a component of the parasite's mitochondrial electron transport chain, and is one of only three protein-coding genes carried on the Plasmodium mitochondrial genome alongside cox3 and cob, an arrangement completely conserved across 23 Plasmodium species (PMID:8459834, PMID:21329764). The gene resides on the 6-kb extrachromosomal mitochondrial DNA and, in P. yoelii, is transcribed as a discrete ~1.4 kb RNA during erythrocytic stages, with a defined 12-nucleotide 5' sequence element and a 3' stem-loop that marks the end of the open reading frame and functions as a putative transcription termination signal (PMID:1701017). Functionally, COX1 is predicted to be the recipient of copper at its CuB site from the assembly factor PfCox11, whose copper-binding activity was mapped to cysteine 157 in vitro (PMID:35672733). Direct enzymatic characterization of the COX1 subunit itself has not been demonstrated in the available corpus; its structural assignment rests on sequence similarity to COX1 orthologs in other species (PMID:8459834).

1. 1990 Medium

   Establishing where cox1 is encoded and how it is expressed was required to place COX1 within the parasite's mitochondrial genetic system; RNA-level characterization showed it is transcribed as a discrete unit with defined boundaries.

   Evidence Primer extension, RNA sequencing, and Northern blot of erythrocytic-stage P. yoelii parasites

   PMID:1701017

   Open questions at the time

   • Whether the 5' element and 3' stem-loop mediate transcription initiation and termination was inferred from position, not tested functionally
   • Transcript processing and translation of the COX1 protein were not characterized
   • Shown in P. yoelii; not confirmed for the P. falciparum ortholog
2. 1993 Low

   Determining the coding identity of the P. falciparum 6-kb mitochondrial element assigned COX1 to the electron transport chain by sequence, establishing the gene's presumptive molecular role.

   Evidence DNA sequencing and comparative structural analysis of the predicted COX1 polypeptide from the P. falciparum 6-kb mitochondrial element

   PMID:8459834

   Open questions at the time

   • No direct functional or enzymatic assay of the COX1 subunit was performed
   • Assignment rests solely on sequence similarity to other species
   • Assembly into a cytochrome c oxidase complex was not demonstrated
3. 2011 Low

   Comparative genomics across the genus tested whether the cox1 gene content and arrangement are conserved, establishing it as a stable, core feature of the minimal Plasmodium mitochondrial genome.

   Evidence Comparative sequencing and bioinformatic analysis of mitochondrial genomes from 23 Plasmodium species

   PMID:21329764

   Open questions at the time

   • Conservation was assessed at the sequence level only, with no functional correlate
   • Does not establish the enzymatic activity or essentiality of COX1
4. 2022 Low

   Characterizing the copper-delivery assembly factor PfCox11 provided indirect functional context for COX1 by identifying the presumed source of copper for its CuB catalytic site.

   Evidence Recombinant PfCox11 expression, in vitro copper-binding assays, and site-directed mutagenesis identifying Cys157 as important for copper binding

   PMID:35672733

   Open questions at the time

   • Copper transfer to COX1 itself was inferred by analogy to yeast, not directly demonstrated for the Plasmodium protein
   • The functional characterization is of the assembly factor, not COX1
   • No reconstitution of copper loading onto the COX1 CuB site

• Direct biochemical proof that the Plasmodium COX1 polypeptide is a catalytically active cytochrome c oxidase subunit remains unestablished.
• No direct enzymatic assay of the COX1 subunit
• No structural verification of copper loading at the CuB site in the parasite protein
• No genetic demonstration of COX1 function or essentiality in blood-stage parasites