are double membrane-bounded organelles that exert essential metabolic functions such as the synthesis of iron-sulfur
clusters. Since most of the mitochondrial proteins are encoded
in the nucleus, they have to be imported into one of the
four mitochondrial compartments (Fig. 1).
1: Current simplified model of six different mitochondrial protein
import pathways. The model is mainly based on numerous studies
in yeast, bread mold and mammals but needs to be revised for parasitic protists (Eckers
et al. 2012a).
whether the compartment is the outer membrane (OM), the
intermembrane space (IMS), the inner membrane (IM) or the
matrix, cytosolic proteins enter the mitochondria of yeast and other opisthokonts via the
TOM complex. From there they use different protein import
machineries including the TOB/SAM complex, the small Tim
proteins, the Mia40/Erv1 system, the TIM23 complex or the
components Tim22 and Oxa1. We are interested in various
aspects of the mitochondrial protein import of parasitic
protists. The following questions are addressed:
How conserved is the mitochondrial protein import
Which of the components are present and isofunctional
Do some parasites have alternative components or transport systems?
Which residues are essential in isofunctional
What are the exact functions of these residues?
favourite pet is the unicellular parasite Leishmania
tarentolae, which can be easily cultured and manipulated
(Fig. 2). Although L. tarentolae is absolutely harmless (unless you
are a gecko from Africa), it is closely related to other
kinetoplastida, including important human pathogens such
as L. donovani (causing kala azar),
Trypanosoma brucei (sleeping sickness) and
T. cruzi (Chagas disease). One advantage and interesting feature of the L. tarentolae mitochondrion is its strong
autofluorescence, which can be used, for example, for co-localization studies (Eckers
et al. 2012b). Furthermore, when we established L. tarentolae as a non-opisthokont
model organism for mitochondrial import, we were able to demonstrate that the different mitochondrial import signals from Fig. 1 are functionally conserved among eukaryotes
despite significant compositional differences of the protein import machineries (see Eckers
et al. 2012a).
2: Liquid cultures and agar plates with L. tarentolae insect
stages in our lab.
We also work with selected candidate genes of the mitochondrial transport machinery from the human malaria parasite Plasmodium falciparum (reviewed in Deponte
et al. 2012 and Deponte 2014).
The components form L. tarentolae and P. falciparum are analyzed in vitro and by complementation studies in yeast. For example, we could show that parasite homologues of Erv1/ALR (Fig. 1, Deponte and Hell 2009)
are functional sulfhydryl:cytochrome c oxidoreductases that localize to the mitochondrial intermembrane space.
We also showed that Erv homologues from kinetoplastid parasites have an altered catalytic mechanism (Eckers
et al. 2013). However, it is not the altered catalytic mechanism but the presence of a single cysteine residue that renders L. tarentolae Erv incompatible with Mia40 from yeast (Specht
et al. 2018). The physiological role of this partially conserved cysteine residue and the identity of the protein that fulfills the functions of Mia40 in parasitic protists still remain unknown.
project is currently funded by the DFG(grant DE 1431/10). Previous funding was provided by the DFG
(grant DE 1431/2), the Friedrich-Baur-Stiftung,
and the Bavaria California Technology Center.