Genetic and Biochemical Dissection of Phospholipid Transport to the Mitochondria
Abstract
How phospholipids are transported to different organelles within the cell is a major unsolved question in cell biology. To address this gap in knowledge, I utilized Saccharomyces cerevisiae as a model organism to study phospholipid trafficking to the mitochondria. I mainly focused on identifying genes required for phosphatidylserine (PS) and phosphatidylethanolamine (PE) transport to the mitochondria since they are essential for the mitochondrial respiratory chain (MRC).
Through genetic and biochemical analysis of inter-organelle membrane tethering complexes, I discovered that Vps39, a protein involved in vacuole to mitochondria contact site formation as well as vesicular fusion, is essential for PE transport from the endoplasmic reticulum (ER) to the mitochondria. I showed that the loss of Vps39 specifically abrogates the transport of PE to the mitochondria without compromising its biosynthesis in the ER or its transport to other subcellular organelles. The recruitment of Vps39 to the ER and mitochondria is dependent on the PE levels of these organelles, directly implicating Vps39 in PE transport. Furthermore, I identified the essential domains of the Vps39 protein required for its PE transport functions and provided evidence that the role of Vps39 in intracellular PE trafficking is independent of its known roles in contact site formation and vesicular trafficking.
In addition to PE transport from the ER to the mitochondria, I discovered that Vps39 is also essential for PE transport from the endosomes to the mitochondria. The endosomal PE transport to PE-deficient mitochondria is triggered in response to phosphatidylcholine (PC) biosynthesis from choline, which obviated the need of PC biosynthesis from endosomal PE. In this manner, choline supplementation is able to rescue mitochondrial respiration in PE deficient cells.
Mitochondria can also biosynthesize PE in situ from phosphatidylserine (PS), which has to be imported from the ER. However, PS import to the mitochondria is not fully understood. I designed and performed a genome-wide screen using yeast deletion mutants to identify genes required for PS transport to the mitochondria. This experiment has yielded a number of novel candidates of mitochondrial PS import. Together, the research in this dissertation identifies novel genes in phospholipid trafficking to the mitochondria.
Subject
phospholipidtransport
phosphatidylethanolamine
phosphatidylcholine
phosphatidylserine
Vps39
Citation
Iadarola, Donna Marie (2021). Genetic and Biochemical Dissection of Phospholipid Transport to the Mitochondria. Doctoral dissertation, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /195654.