| Abstract |
The biogenesis of mitochondria is based on specific pathways for targeting and
import, as most proteins are synthesized in the cytoplasm and subsequently enter the
different compartments. The discovery of the oxidative folding pathway in
mitochondria, MIA, in 2004 was a turning point in the history of these organelles.
Following studies have focused mainly on the small typical substrates of the pathway
and the interactions of the two central partners, the redox controlled receptor Mia40
and the sulfydryl-oxidase Erv1. Great progress has been made in the recent years, as
the list of the proteins that utilize the pathway is constantly expanding with larger and
more complex substrates, including Mia40 itself.
In this work, we studied three different proteins and their function in the
mitochondrial intermembrane space. In the first chapter, we focused on the
oxidoreductase Mia40, its characteristics as a substrate and dissected precisely the
stages of its biogenesis in yeast. Our results illustrate a coordinated sequence of
events, and are summarized with import of the Mia40 precursor into mitochondria
anchored into the inner membrane translocase, interaction with the endogenous active
Mia40 for folding of the structural core of the molecule and finally oxidation of the
catalytic center by Erv1. These two kinetically distinct interactions are based on
completely different determinants with Mia40 presenting an atypical behavior
compared to other substrates that utilize the mitochondrial oxidative pathway.
The second chapter describes the study of the peroxidase Gpx3 in the intermembrane
space. It was already known that this protein acts in the cytosol as a sensor for redox
stress and signal transducer for the response against it. Recently, it was shown that it
can also be located in the intermembrane space of mitochondria without evidence or
any description of the conditions that lead to this localization. Our results suggest that
mitochondria host a putative redox regulation pathway with Gpx3 as the key
component.
For this study, we evaluated protein interactions focusing mainly on the receptor of
this compartment, Mia40, using different assays (in vivo, in organello, in vitro) to
build a model that will explain its role in mitochondria. This is an ongoing project and
collaboration with the group of Chris Grant (University of Manchester) with
experiments conducted by Paraskeui Kritsiligkou. In the third chapter, we focused on the protein Dre2, whose function is associated
with the cytosolic maturation pathway of iron/sulfur cluster proteins (CIA). The
localization of this protein in the intermembrane space of mitochondria is supported
by two different scientific groups and was further investigated in this work. In
addition, we studied its interaction with Mia40, which is the second indication of the
connection of the disulfide exchange pathway with the export pathway for iron/sulfur
clusters that is also hosted in the same compartment. The first indication of the
association of the MIA pathway in the Fe/S cluster biogenesis was the participation of
Erv1 in the ISC export. Finally, in this project we set the basis for studying the
potential role of Dre2 as a mediator of the two mitochondrial pathways.
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Βιογένεση πρωτεϊνών και οξειδωτική αναδίπλωση στα μιτοχόνδρια
