CeBiTec – Colloquium
Tuesday, January 9, 2018, 17 c.t.
G2-104, CeBiTec Building
Dr. Jennifer Selinski
ARC Centre of Excellence in Plant Energy
Biology School of Life Science
La Trobe University,  Bundoora (Australia)
Isoform-specific differences between Alternative Oxidase proteins
The cyanide-insensitive alternative oxidase (AOX) is a non-proton-pumping ubiquinol oxidase that allows plants to respire without mitochondrial ATP production, improving plant performance under adverse growth conditions. AOX catalyzes the reduction of oxygen to water and is post-translationally regulated by redox mechanisms and 2-oxo acids.
Arabidopsis thaliana possesses five AOX isoforms (AOX1A-D and AOX2). AOX1D expression is increased in aox1a knock-out mutants from A. thaliana (especially after restriction of the cytochrome c pathway), but cannot compensate for the lack of AOX1A, suggesting a difference in regulation of these isoforms. Therefore, we analysed the different AOX isoenzymes with the aim to identify differences in their post-translational regulation.
At the protein level, AOX activity is mainly negatively controlled. Its primary structure is not optimal for activity since changes in a single amino acid dramatically increases activity. Furthermore, the activity can be largely increased via various metabolites, e.g. TCA-cycle intermediates that act in an isoform-specific manner. Various tricarboxylic acid cycle intermediates were tested for their influence on AOX1A, AOX1C, and AOX1D wild-type protein activity, using a refined in vitro system. AOX1C is insensitive to all tested organic acids, AOX1A and AOX1D are both activated by 2-oxoglutarate, but only AOX1A is additionally activated by oxaloacetate.
In summary, we show that AOX isoforms from Arabidopsis are differentially fine-regulated by TCA cycle metabolites (most likely depending on the N-terminal region around the highly conserved cysteine residues known to be involved in regulation by the 2-oxo acids pyruvate and glyoxylate) and propose that this is the main reason why they cannot functionally compensate for each other.
Host: Prof. Dr. Bernd Weisshaar