Mitochondria are dynamic organelles involved in a variety of cellular processes, such as energy. Mitochondria can also orchestrate cell death (apoptosis) via release of cytochrome c and activation of the caspase signalling cascade. Cancer cells often display misregulation in apoptosis, contributing to the generation of chemotherapy-resistant cells. Thus, mitochondria are at the centre of a plethora of cellular processes both under normal physiological circumstances and in disease. Phospholipid composition plays an important role in mitochondrial homeostasis. Changes in lipid content and structure have been associated with mitochondrial dysfunction and a variety of diseases including ischemia, hypothyroidism, aging, and heart failure. The family proteins (Ups1-3 in yeast and PRELIs in humans) together with a novel CX9C chaperone (Mdm35 in yeast and TRIAP1 in humans) regulate the accumulation of phospholipids within mitochondrial membranes. This pathway has been shown to be important for modulating apoptotic through two independent mechanisms. One indirectly through resultant increased cardiolipin accumulation and sequestration of cytochrome C, which is required for apoptosome formation. The other is through a direct interaction with Hsp70 and APAF1 thereby preventing cytochrome C from assembling in the apoptosome. These mechanisms stall apoptosis and gives cell to the opportunity to repair DNA damage This proposal aims to characterize the structure and interactions of human TRIAP1/PRELI using NMR and X-ray crystallography approaches. The structural and dynamic properties of TRIAP1 with PRELI proteins and Hsp70 will be probed by site-directed mutagenesis and functional assay. The outcomes of this research project will provide new insight into the biological roles for the TRIAP1/Mdm35 family of proteins, which have been implicated in mitochondrial lipid homeostasis and cytotoxic drug-resistance through the evasion of apoptosis.