COX2b

COX2b is a nuclear-encoded subunit of the mitochondrial cytochrome c oxidase (Complex IV) in Toxoplasma gondii, where it localizes to the parasite mitochondria and, together with COX2A, co-migrates with the assembled Complex IV on Blue Native/2D electrophoresis and is identified in that complex by mass spectrometry (PMID:18036550). Mitochondria-enriched fractions containing this complex support cyanide-sensitive oxygen uptake, placing COX2b within the functional respiratory chain (PMID:18036550). Beyond this localization and complex-association evidence, no further mechanistic detail — including genetic loss-of-function characterization — has been established in the available corpus.

1. 2007 Medium

   The question of which subunits constitute Toxoplasma Complex IV was addressed by showing COX2B is a mitochondrial subunit that physically associates with the assembled, respiration-competent enzyme.

   Evidence Anti-recombinant COX2B antibody immunolocalization, mitochondrial fractionation, Blue Native PAGE with 2D electrophoresis, MS identification, and cyanide-sensitive oxygen uptake assay

   PMID:18036550

   Open questions at the time

   • No genetic loss-of-function to demonstrate that COX2B is required for Complex IV assembly or activity
   • The molecular role of COX2B within the complex (e.g. catalytic contribution, structural stabilization) is not defined
   • The relationship between COX2A and COX2B, and why the subunit is split, is not resolved

• Whether COX2B is functionally essential and its specific mechanistic contribution to Complex IV catalysis remain unresolved.
• No conditional knockout or knockdown phenotype
• No structural model of the T. gondii Complex IV incorporating COX2B
• Import and assembly pathway of the nuclear-encoded subunit not characterized