Membranes and Bioenergetics
Sulfide-Quinone Reductase from Rhodobacter capsulatus: PURIFICATION, CLONING, AND EXPRESSION*

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A sulfide-quinone oxidoreductase (SQR, EC 1.8.5.′.) has been purified to homogeneity from chromatophores of the non-sulfur purple bacterium Rhodobacter capsulatus DSM 155. It is composed of a single polypeptide with an apparent molecular mass of about 55 kDa, exhibiting absorption and fluorescence spectra typical for a flavoprotein and similar to the SQR from the cyanobacterium Oscillatoria limnetica

From N-terminal and tryptic peptide sequences of the pure protein a genomic DNA clone was obtained by polymerase chain reaction amplification. Its sequence contains an open reading frame of 1275 base pairs (EMBL nucleotide sequence data base, accession no. X97478) encoding the SQR of R. capsulatus The deduced polypeptide consists of 425 amino acid residues with a molecular mass of 47 kDa and a net charge of +9. The high similarity (72%)/identity (48%) between the N termini of the cyanobacterial and the bacterial enzyme was confirmed and extended. Both enzymes exhibit the FAD/NAD(P) binding βαβ-fold (Wierenga, R. K., Terpstra, P., and Hol, W. G. S. (1986) J. Mol. Biol. 187, 101-107). The complete sequence of the SQR from R. capsulatus shows further similarity to flavoproteins, in particular glutathione reductase and lipoamide dehydrogenase. The cloned sqr was expressed in Escherichia coli in a functional form.

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This work was supported in part by the Deutsche Forschungsgemeinschaft (DFG) and the Moshe Shilo Center for Marine Biogeochemistry (Israel). The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The nucleotide sequence(s) reported in this paper has been submitted to the GenBank™/EMBL Data Bank with accession number(s) X97478.

© 1997 ASBMB. Currently published by Elsevier Inc; originally published by American Society for Biochemistry and Molecular Biology.