Deciphering the Kynurenine-3-Monooxygenase Interactome

Kynurenine-3-monooxygenase (KMO) is a mitochondrial enzyme in the kynurenine pathway (KP) through which tryptophan is degraded to NAD+. The central KP is altered in neurodegenerative diseases and other CNS disorders. The causative role of KP metabolites has been particularly well studied in the neurodegenerative disorder Huntington’s disease (HD), a fatal adult onset condition inherited in an autosomal dominant manner. In HD, flux in the KP is perturbed such that neurotoxic metabolites (3-hydroxykynurenine and quinolinic acid) of the pathway are increased relative to a neuroprotective metabolite (kynurenic acid). KMO lies at a critical branching point in the KP such that inhibition of KMO activity ameliorates this metabolic perturbation. Consequently, several recent studies have found that KMO inhibition is protective in models of HD. These findings have widespread implications in treating several neurodegenerative diseases such as Alzheimer’s disease and Parkinson’s disease where the KP is implicated in pathogenesis. The focus of this project was to better understand the cellular role(s) and interactions of KMO. To this end, a novel membrane yeast two hybrid approach was established and optimised to identify protein interaction partners for outer mitochondrial membrane proteins. This approach was implemented to identify protein interaction partners of human KMO and its yeast orthologue Bna4, which were confirmed by biochemical approaches. Additionally, genetic interaction partners of BNA4 identified by systematic genetic screens were individually validated by classic genetic manipulations. Bioinformatic tools were then used to identify enriched interaction networks for KMO using this novel interaction data. These analyses suggested possible roles for KMO in many processes, including energy metabolism, cytoskeleton organisation and response to infection and inflammation, providing evidence that KMO plays roles in diverse cellular pathways in addition to the KP.