Verlag des Forschungszentrums Jülich
JUEL-4032
Niebisch, Axel
Molekulare Charakterisierung des Cytochrom -bc1-aa3-Superkomplexes aus Corynebacterium glutamicum
IV, 106 S., 2003
Spektroskopische Untersuchungen und Inhibitorstudien deuteten auf eine verzweigte Atmungskette
in Corynebacterium glutamicum hin, bei der der Elektronenfluß von Menachinol
auf Sauerstoff entweder über einen Cytochrom-bcl-Komplex und eine Cytochrom-c-Oxidase
des aa3-Typs oder alternativ über eine Menachinoloxidase des bd-Typs verlaufen kann. Diese
Arbeit hatte eine molekulare Charakterisierung des postulierten bcl-aa3-Zweigs zum Ziel.
Spectroscopical investigations and inhibitor studies indicated a branched respiratory chain in
Corynebacterium glutamicum. Electrons can be transferred to oxygen either via a cytochrome
bcl complex and a aa3-type cytochrome c oxidase or alternatively via a menaquinol oxidase
of the cytochrome bd-type. The aim of this work was a molecular characterization of the postulated
bcl-aa3-branch . The genes of the three subunits of the bcl complex (gcrCAB) and of
subunits I and III of cytochrome aa3 oxidase (ctaD and ctaE) were cloned and sequenced .
Analysis of the deduced protein sequences showed a number of unusual features. The Rieske
iron sulfur protein (QcrA) had three putative N-terminal transmembranhelices and cytochrome
b (QcrB) possessed a large C-terminal domain consisting of approximately 130 amino
acids in addition to the conserved part ofthe protein. Most remarkably, cytochrome cl (QcrC)
contained two CXXCH motifs for covalent heme binding indicating that this protein is a diheme-
cytochrome c. Inactivation of the bcl complex or the cytochrome aa3 oxidase by chromosomal
deletion of the qcr genes and the ctaD gene, respectively, led to strongly impaired
aerobic growth an glucose minimal medium indicating that the bcl-aa3-pathway is the main
route of respiratoon under these conditions. Cytochrome b (QcrB) and subunit I of cytochrome
aa3 oxidase (CtaD) were elongated with a C-terminal StrepTag II and purified by affmity
chromatography an StrepTactin sepharose. In both cases a bcl-aa3-supercomplex was obtained
which possessed quinol oxidase activity and therefore represented a functional association
of bcl complex and cytochrome aa3 oxidase. Mutation of the cysteine residues in either
heme binding motifs of cytochrome cl (QcrC) led to a similar phenotype like deletion of the
qcr genes. No c-type cytochrome could be detected in membranes of both strains and their
QcrB content was strongly reduced. Obviously both heme binding motifs of QcrC are essential
for activity, assembly and/or stability ofthe bcl complex.
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