RAPISARDA Viviana Andrea
congresos y reuniones científicas
Cellular Cu(II)-reduction by E. coli respiratory chain in copper exporters deficient strains
VOLENTINI, S. I.; SCHURIG-BRICCIO, L. A.; RINTOUL, M. R.; FARIAS, R. N.; RODRÍGUEZ MONTELONGO, L.; RAPISARDA, V. A.
Carlos Paz (Córdoba)
Congreso; XLIV Reunión Anual de SAIB; 2008
Copper is both an essential nutrient and a toxic element able to catalyze free radical formation. In E. coli there are two copper exporters: a P-type ATPase CopA and a multi-component transport system CusCFBA. All proteins of the copper homeostatisis use Cu(I), although the copper reductase activity is still unclear. Previous results of our laboratory have shown that electron flow through the E. coli respiratory chain promotes the reduction of cupric ions by NADH dehydrogenase-2 and quinones. Here we measured Cu(II)-reduction as the rate of Cu(I) appearance in supernatant of cellular suspensions exposed to sub-lethal Cu(II) concentrations using strains lacking several respiratory chain components and/or copper exporters. Without CopA or Cus system, the Cu(II)-reduction rate decreased around 50% respect to the wild-type strain. In the absence of NDH-2, this decrease was nearly 10%, but interestingly a double mutant lacking CopA and NDH-2 recovered the reduction level of the wild-type. In the absence of quinones, the Cu(II)-reduction rate decreased 60-80%. To understand the mentioned events, membranes NADH and D-Lactate:Cu(II)-oxidoreductase activities of different mutants were assayed. We proposed two copper reduction mechanisms in E. coli: one of them occurs in cytoplasm and is mediated by both NDH-2 and quinones and the other to the periplasmic side and is mediated only by quinones.