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DsrJ, an Essential Part of the DsrMKJOP Transmembrane Complex in the Purple Sulfur Bacterium Allochromatium vinosum, Is an Unusual Triheme Cytochrome c
Zitatschlüssel Grein2010
Autor Grein, Fabian and Venceslau, Sofia S. and Schneider, Lilian and Hildebrandt, Peter and Todorovic, Smilja and Pereira, Ines A. C. and Dahl, Christiane
Seiten 8290-8299
Jahr 2010
ISSN 0006-2960
DOI 10.1021/bi1007673
Adresse 1155 16TH ST, NW, WASHINGTON, DC 20036 USA
Jahrgang 49
Nummer 38
Monat SEP 28
Zusammenfassung The DsrMKJOP transmembrane complex has a most important function in dissimilatory sulfur metabolism, not only in many sulfur-oxidizing organisms but also in sulfate-reducing prokaryotes. Here, we focused on an individual component of this complex, the triheme cytochrome c DsrJ from the purple sulfur bacterium Allochromatium vinosum. In A. vinosum, the signal peptide of DsrJ is not cleaved off but serves as a membrane anchor. Sequence analysis suggested the presence of three heme c species with bis-His, His/Met, and possibly a very unusual His/Cys ligation. A. vinosum DsrJ produced as a recombinant protein in Escherichia coli indeed contained three hemes, and electron paramagnetic resonance (EPR) spectroscopy provided evidence of possible, but only partial, His/Cys heme ligation in one of the hemes. This heme shows heterogeneous coordination, with Met being another candidate ligand. Cysteine 46 was replaced with serine using site-directed mutagenesis, with the mutant protein showing a small decrease in the magnitude of the EPR signal attributed to His/Cys coordination, but identical UV-vis and RR spectra. The redox potentials of the hemes in the wild-type protein were determined to be -20, -200, and -220 mV and were found to be virtually identical in the mutant protein. However, in vivo the same ligand exchange led to a dramatically altered phenotype, highlighting the importance of Cys46. Our results suggest that Cys46 may be involved in catalytic sulfur chemistry rather than electron transfer. Additional in vivo experiments showed that DsrJ can be functionally replaced in A. vinosum by the homologous protein from the sulfate reducer Desulfovibrio vulgaris.
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