MitoPNP · Structural and functional studies of human PNPase in mitochondrial RNA metabolism

Throughout the eukaryotic lineages, mitochondria are essential organelles that provide cellular metabolic power through oxidative phosphorylation. In the mitochondrial intermembrane space resides an exoribonuclease highly conserved in the course of evolution: PNPase. Although the activity of this enzyme has been extensively studied, its function in this compartment is poorly understood. A clue to one of its potential functions has been provided by my recent findings on the bacterial PNPase, which I discovered to switch activity from an RNA degradation mode to a stabilising mode that chaperones regulatory RNAs. As the human and bacterial enzymes are homologues, it is possible that human PNPase (hPNPase) could have a dual mode of action as well, and could participate in regulatory processes or RNA cargo transport once trapped in a non-degradative assembly. My research will address what functions are played by hPNPase present in the intermembrane space of the human mitochondria. I will characterise the full-length enzyme and its capacity to bind substrates in the degradative and non-degradative modes. In order to achieve these objectives, I will elucidate the structure-function relationship of hPNPase by cryo-electron microscopy complemented with biochemical and biophysical assays. The results will illuminate the biological roles of PNPase in human cells including its potential contributions to mitochondrial RNA trafficking. This interdisciplinary project with potential applications in human health will apply recent breakthrough advancements in cryo-EM in order to investigate the molecular basis of an intricate biological system to advance the understanding of mitochondria biology. The research effort will foster the career development of a talented researcher and contribute to the academic and research excellence in Poland by strengthening the expertise in cryo-EM, a method currently revolutionising structural biology, at the University of Warsaw.