dc.description.abstracteng | Mitochondrial diseases are fatal disorders
mainly affecting highly energy dependent tissues such as brain,
heart, liver and muscle. These severe disorders can be caused by
mutations affecting mitochondrial- or nuclear-encoded proteins. The
molecular function of many nuclear-encoded mitochondrial proteins
involved in disease is unknown so far and therefore, the mechanisms
that lead to disease are enigmatic. In this study, point mutations
in SURF1 and MPV17 were analyzed that were found in patients of the
Leigh Syndrome and the Mitochondrial DNA Depletion Syndrome
respectively. These missense mutations affect highly conserved and
therefore potentially functional important amino acids.
The function of SURF1, a highly conserved early assembly factor of
the cytochrome c oxidase, has been studied using its yeast homolog
Shy1. Shy1 is involved in the maturation and translational feed
back regulation of Cox1, the central subunit of the cytochrome c
oxidase. In this study, it was shown that patient point mutations
affecting G124 in SURF1 lead to rapid degradation of the protein
after mitochondrial import. In contrast, patient mutations that
lead to an Y274D exchange in SURF1 do not alter mitochondrial
import or stability but showed increased association to a newly
identified cytochrome c oxidase assembly intermediate. Hence,
SURF1Y274D shows impaired function. Using the corresponding yeast
Shy1Y344D as a model, dual functionality of SURF1/Shy1 could be
shown. Shy1Y344D releases cytochrome c oxidase assembly
intermediates from translational feed back regulation of Cox1 but
fails to promote cytochrome c oxidase assembly at later
steps.
Mutations affecting MPV17, a mitochondrial inner membrane protein
of previously unknown function, lead to loss of mitochondrial DNA.
In this study Sym1, the yeast homolog of MPV17, was used as a model
to study the biogenesis and function of MPV17/Sym1. It could be
shown that Sym1 forms high molecular weight complexes of 120 and
220 kDa in the mitochondrial inner membrane. In contrast to most
polytopic inner membrane proteins, Sym1 is imported in a TIM23
dependent manner into mitochondria. The function of Sym1 was
analyzed by electrophysiological characterization of Sym1, isolated
from yeast mitochondria. Sym1 showed channel activity, which
indicates a pore forming function of Sym1/MPV17 in the
mitochondrial inner membrane. | de |