Biomedical Engineering Reference
In-Depth Information
Chapter 3
Import of Proteins into Isolated Yeast Mitochondria
Valentina Peleh, Ajay Ramesh, and Johannes M. Herrmann
Abstract
Mitochondria are essential organelles of eukaryotic cells. The vast majority of mitochondrial proteins is
encoded within the nuclear genome and translocated into various mitochondrial compartments after trans-
lation in the cytosol as preproteins. Even in rather primitive eukaryotes like yeasts, there are 700-1,000
different proteins that need to be recognized in the cytosol, directed to the protein translocases in the two
mitochondrial membranes and sorted to their appropriate mitochondrial subcompartment. In vitro recon-
stituted import systems have proved to be important tools to study these processes in detail. Using isolated
mitochondria and radioactively labeled precursor proteins, it was possible to identify several import
machineries and pathways consisting of a large number of components during the last few decades.
Key words
Cell-free protein synthesis, In vitro import, Mitochondria, Protein translocation,
Saccharomyces cerevisiae
1
Introduction
Mitochondria are complex double-membrane bounded organelles
that exhibit a huge variety of functions. Besides their role in cellular
respiration, mitochondria participate in biochemical key processes
like synthesis of metabolites, lipid metabolism, free radical produc-
tion, apoptosis and metal homeostasis [
1
]. Depending on the
organism, mitochondria contain about 500-2,000 different
proteins [
2
-
4
]. In the yeast
Saccharomyces cerevisiae
, only eight of
these proteins are encoded by mitochondrial DNA. All the remain-
ing proteins are encoded in the nucleus and synthesized on
cytosolic ribosomes. Following synthesis as precursor proteins
(preproteins) they have to be imported into the organelle (for
review
see
ref.
5
-
7
). Mitochondria can be divided into four func-
tionally specialized subcompartments: the outer membrane, the
intermembrane space (IMS), the inner membrane, and the matrix.
Precursor proteins access one of these different compartments as
their final location by the use of specific targeting signals. Targeting
signals are recognized by receptors on the surface of the organelle.
Bor Luen Tang (ed.),
Membrane Trafficking: Second Edition
, Methods in Molecular Biology, vol. 1270,
DOI 10.1007/978-1-4939-2309-0_3, © Springer Science+Business Media New York 2015
37
