Human, plant and yeast cells all contain mitochondria, which provide energy to their respective cells. Surrounded by inner and outer membranes as well as space between which contain enzymes which perform various metabolic processes, mitochondria are an integral component of life in every cell. Proteins created in the cytoplasm are transported into mitochondrial intermembrane space where they acquire disulfide bonds to fold correctly and form functional tetramers within mitochondrion. This process is orchestrated by two proteins known as mitochondrial disulfide relay (also called MIA pathway) and Mia40; its CPC motif serves as a protein trap and plays a crucial role in the oxidative folding step of this process.
This study shows that Mia40’s CPC motif is not necessary for mitochondrial protein import and can be replaced with interaction with hydrophobic regions of proteins. Furthermore, disulfide bond formation isn’t essential in order to facilitate transport into mitochondria; instead its mechanism could apply more widely across other protein import pathways in cells.
To understand the role of hydrophobic domain, a 10CS peptide was created by removing CPC residues from Mia40-SPS and Mia40-FE and incubating it with tyrosine protein synthase for 1 minute. This protein was then examined for its ability to promote import of radiolabeled tyrosine-tagged cytochrome b2 into mitochondria using an in vitro import assay; results revealed that this tyrosine peptide effectively promoted binding but did not result in back translocation into cytosol or back into cells.