Mol Microbiol. 2011 Aug 19. doi: 10.1111/j.1365-2958.2011.07807.x. [Epub ahead of print]
Two internal type II NADH dehydrogenases of Toxoplasma gondii are both required for optimal tachyzoite growth
Lin SS, Gross U, Bohne W
SourceInstitute of Medical Microbiology, University Medical Center Göttingen, Kreuzbergring 57, Göttingen D-37075, Germany.
In many apicomplexan parasites the entry of electrons from NADH into the electron transport chain is governed by type II NADH dehydrogenases (NDH2s) instead of a canonical complex I. Toxoplasma gondii expresses two NDH2 isoforms, TgNDH2-I and TgNDH2-II with no indication for stage-specific regulation. We dissected the orientation of both isoforms by using a split GFP assay and a protease protection assay after selective membrane permeabilization. The two approaches revealed that both TgNDH2 isoforms are internal enzymes facing with their active sites to the mitochondrial matrix. Single knock-out mutants displayed a decreased replication rate and a reduced mitochondrial membrane potential, which were both more severe in the Tgndh2-II-deleted than in the Tgndh2-I-deleted mutant. Complementation with a myc-tagged, ectopic copy of the deleted gene restored the growth rate and the mitochondrial membrane potential. However, an over-expression of the remaining intact isoform could not restore the phenotype, suggesting that the two TgNDH2 isoforms are non-redundant and possess functional differences. Together, our studies indicate that although TgNDH2-I and TgNDH2-II are individually non-essential, the expression of both internal isoforms is required to maintain the mitochondrial physiology in T. gondii tachyzoites.
© 2011 Blackwell Publishing Ltd.
PMID:21854467[PubMed - as supplied by publisher]