Mito be more than a power house: structural and functional analysis of the human mitochondrial acyl carrier protein (mACP) and ketosynthase (OXSM)

Outside of their involvement in energy production, mitochondria play a critical role in cells through their access to a discrete fatty acid biosynthetic pathway. While human mitochondria import some fatty acids from the cytoplasm for energy production through β-oxidation, its fatty acid synthase (FAS) pathway is considered the sole system for producing fatty acid moieties within mitochondria for lipoic acid synthesis and membrane lipid modification. Despite decades of study in bacterial FASs (the putative evolutionary mitochondrial precursor), our understanding of human mitochondrial fatty acid biosynthesis remains incomplete. In our studies, we established a robust and scalable method for the recombinant expression and purification of mACP, ensuring access to the protein for activity and biophysical studies. The elemental behaviors of mACP, substrate sequestration and chain flipping, were explored using solvatochromism, an environmentally sensitive fluoresce. This provides an efficient approach toward understanding the fundamental protein−protein interactions (PPIs) of mACP and its partner proteins. Furthermore, by leveraging the mechanism-based crosslinking probes developed in our lab, we successfully conducted structural biological studies to analyze the structures and the essential PPIs between mACP and its partner protein 3-oxoacyl-ACP synthase (OXSM) via x-ray crystallography for the very first time. Understanding these interactions may offer insights into genetic mitochondrial diseases implicating FAS, ultimately assisting therapeutic development.