title: Non-enzymic copper reduction by menaquinone enhances copper toxicity in Lactococcus lactis IL1403.
abstract: Lactococcus lactis possesses a pronounced extracellular Cu(2+)-reduction activity which leads to the accumulation of Cu(+) in the medium. The kinetics of this reaction were not saturable by increasing copper concentrations, suggesting a non-enzymic reaction. A copper-reductase-deficient mutant, isolated by random transposon mutagenesis, had an insertion in the menE gene, which encodes O-succinylbenzoic acid CoA ligase. This is a key enzyme in menaquinone biosynthesis. The ΔmenE mutant was deficient in short-chain menaquinones, and exogenously added menaquinone complemented the copper-reductase-deficient phenotype. Haem-induced respiration of wild-type L. lactis efficiently suppressed copper reduction, presumably by competition by the bd-type quinol oxidase for menaquinone. As expected, the ΔmenE mutant was respiration-deficient, but could be made respiration-proficient by supplementation with menaquinone. Growth of wild-type cells was more copper-sensitive than that of the ΔmenE mutant, due to the production of Cu(+) ions by the wild-type. This growth inhibition of the wild-type was strongly attenuated if Cu(+) was scavenged with the Cu(I) chelator bicinchoninic acid. These findings support a model whereby copper is non-enzymically reduced at the membrane by menaquinones. Respiration effectively competes for reduced quinones, which suppresses copper reduction. These findings highlight novel links between copper reduction, respiration and Cu(+) toxicity in L. lactis.
authors.affiliation: Department Clinical Research, University of Bern, Murtenstrasse 35, 3010 Bern, Switzerland.
authors.forename: Helge K
authors.initials: HK
authors.lastname: Abicht
authors.affiliation: Department of Plant Physiology and Biotechnology, Tomsk State University, Lenin Prospect 36, 634050 Tomsk, Russia.|Department Clinical Research, University of Bern, Murtenstrasse 35, 3010 Bern, Switzerland.
authors.forename: Yulia
authors.initials: Y
authors.lastname: Gonskikh
authors.affiliation: Department Clinical Research, University of Bern, Murtenstrasse 35, 3010 Bern, Switzerland.
authors.forename: Simon D
authors.initials: SD
authors.lastname: Gerber
authors.affiliation: Department Clinical Research, University of Bern, Murtenstrasse 35, 3010 Bern, Switzerland.
authors.forename: Marc
authors.initials: M
authors.lastname: Solioz
mesh_terms: D002462:Cell Membrane / Q000378:metabolism; D003300:Copper / Q000378:metabolism* / Q000633:toxicity*; D004251:DNA Transposable Elements; D055786:Gene Knockout Techniques; D013294:Lactococcus lactis / Q000187:drug effects* / Q000378:metabolism*; D016254:Mutagenesis, Insertional; D010084:Oxidation-Reduction; D013389:Succinate-CoA Ligases / Q000235:genetics; D024482:Vitamin K 2 / Q000378:metabolism*
chemical_list: D004251:DNA Transposable Elements; D024482:Vitamin K 2; D003300:Copper; D013389:Succinate-CoA Ligases; C022693:O-succinylbenzoate - CoA ligase