Regulation of protein import by a thioredoxin reductive pathway in the intermembrane space of mitochondria

[摘要] Mitochondria are organelles that fulfil main roles in cellular metabolism. From the total mitochondrial proteome, 99% of proteins are encoded in the nucleus and have to be imported into mitochondria. Hence, mitochondria have developed at least five import pathways to drive those proteins into the four mitochondrial compartments (the outer and inner membranes, the matrix and the mitochondrial intermembrane space (IMS)). The main pathways are the presequence pathway, the carrier pathway, the β-barrel pathway, the insertion of α-helical proteins and the oxidative folding (MIA) pathway. MIA pathway imports most proteins residing in the IMS by inserting disulfide bridges onto characteristic cysteine motifs in the incoming reduced protein precursors. The import through the MIA pathway depends on the redox homeostasis of the compartments where it takes place, the cytosol and the IMS. This redox homeostasis is the balance between the oxidative and reductive pathways. In particular, the main reductive pathways are the glutaredoxin (Grx) and thioredoxin (Trx) systems, both of which share NADPH as their final electron donor. Despite extensive knowledge on the oxidative pathway, a reducing mechanism in the IMS is yet to be discovered. In this work, we studied the molecular and mechanistic aspects of redox perturbations on the MIA pathway. We found that reductive impairment in the yeast cell specifically decreased the import through the MIA pathway because the key effector, Mia40 is in an unbalanced redox state towards its oxidising form. Furthermore, based on the recent discovery of cytosolic Trx system residing also in the mitochondrial IMS, we investigate its role as this unknown reductive system in this compartment. We found that Trx interacts with Mia 40 and restores its redox state to a functional balanced oxidising and reducing state and that this partially recovers the import capacity of this yeast strain. We conclude by proposing a model in which redox state of Mia40 acts as a sensor of the import of MIA substrates in a Trx-dependent manner.

[发布机构] University:University of Glasgow;Department:Institute of Molecular Cell and Systems Biology

[关键词] Mitochondria biogenesis, import, MIA pathway, redox regulation, thioredoxin sysyem, reducing, oxidation.