Alternative oxidases in animals

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The currency of life on Earth is energy. Living organisms use electron transport systems (ETS) to convert various molecules into adenosine triphosphate (ATP) for growth and reproduction. Cytochrome c oxidase is the final electron acceptor in most ETS, but many organisms also contain a second terminal oxidase called alternative oxidase (AOX). The physiological role for AOX is rather mysterious, as its presence seems counterintuitive from a bioenergetics perspective, but AOX mRNA expression and AOX protein levels increase during stress. These observations suggest that AOX confers flexibility in the ETS and allows organisms to deal with stressful environments. AOX, initially thought to be absent from animals, was discovered in animals in 2005. This new field of research has been explored since then, but there are still significant gaps in our knowledge. I propose to address three main questions that form the basis of my research program. (1) How is AOX post-translationally regulated in animals? Very few studies have looked at a natural AOX protein in animals. The AOX protein is present in several animal species, but our knowledge of the post-translational regulation of the protein's activity in animals is lacking. We will study this process in the copepod Tigriopus californicus, as my lab has spent several years developing tools to study AOX in this organism. We will use high-resolution respirometry to identify the activators and inhibitors of AOX, as well as the impact of potential respiratory substrates on the capacity of this pathway. (2) What is the physiological role(s) of AOX in animals? AOX in plants contributes significantly to stress tolerance by allowing flexibility in the ETS for effective regulation of ATP demand and carbon flux through primary metabolism. Perhaps AOX plays a similar physiological role in animals. We will manipulate the levels of AOX protein in Tigriopus californicus and then will expose these animals to high temperature stress to see if AOX plays a role in their survival under these conditions. (3) What is the taxonomic distribution of AOX in animals? This is a continuing goal of my research program, as it is impossible to study AOX unless we can identify which animals contain it. This work is done by using a combination of bioinformatics analyses to identify animals that contain AOX, followed by molecular biology experiments to confirm the expression of AOX mRNA and the presence of AOX protein in these species. A better understanding of the taxonomic distribution of AOX will contribute to our knowledge on the origin and evolutionary history of the enzyme. The knowledge gained from our research may lead to treatments for human mitochondrial diseases and human infections caused by parasitic animals. Targeting AOX using inhibitors may allow us to kill parasites that threaten Canadian agriculture and aquaculture.