Understanding how the mitochondrial phosphatase PGAM5 regulates mitochondrial dynamics

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Background: Mitochondria are the powerhouse of the cell and are critical mediators of cellular life and death. Many signalling and metabolic pathways are dependent on mitochondrial activity and impact function. One aspect of mitochondrial biology that remains enigmatic is the compelling membrane dynamics that occur within and between mitochondria. Individual units are constantly undergoing membrane fusion and fission reactions, the overall reason for this activity remains unknown. My lab has had a long-standing interest in mitochondrial dynamics, and we have been uncovering proteins and mechanisms that act as regulators. One particularly interesting protein is called PGAM5. PGAM5 is a phosphatase that exists in two isoforms, a long isoform (l-PGAM5) with a mitochondrial targeting and membrane binding motif and a short isoform (s-PGAM5) in which the N-terminus has been removed. It is not currently understood if the isoforms have different functions, but we have recently obtained preliminary data to suggest they have very different roles in regulating mitochondrial membrane dynamics. Hypothesis: l-PGAM5 and s-PGAM5 have both different localizations within mitochondria and regulate different aspects of mitochondrial fusion and fission. Specific aims: 1) Using a variety of cell biological and biochemical approaches, we will determine the inter-organelle localization of the two isoforms of PGAM5, both during cellular homeostasis, and during time of stress when mitochondrial membrane dynamics are required for cellular survival. 2) We will characterize and compare the interactome of the two PGAM5 isoforms using the BioID approach. Lists of potential interactors will be rationalized and validated with secondary approaches including IP and PLA analyses. Our studies should reveal important mechanistic insights into the function of PGAM5 in mitochondrial dynamics. Characterizing differing localizations and protein interactomes should highlight the molecular details of how PGAM5 contributes to mitochondrial biology. In sum these studies should help us to understand the reasons for mitochondrial dynamics as a fundamental aspect of cell biology that is conserved across all eukaryotes.