Two Menkes-type ATPases supply copper for photosynthesis in Synechocystis PCC 6803

Synechocystis PCC 6803 contains four genes encoding polypeptides with seque nce features of CPx-type ATPases, two of which are now designated pacS and ctaA, We show that CtaA and PacS (but not the related transporters, ZiaA or CoaT) facilitate switching to the use of copper (in plastocyanin) as an al ternative to iron (in cytochrome c(6)) for the carriage of electrons within the thylakoid lumen. Disruption of pacS reduced copper tolerance but enhan ced silver tolerance, and pacS-mediated restoration of copper tolerance was used to select transformants, Disruption of ctaA caused no change in coppe r tolerance but reduced the amount of copper cell(-1). In cultures suppleme nted with 0.2 muM copper, photooxidation of cytochrome c(6) (PetJ) was depr essed in wild-type cells but remained elevated in both Synechocystis PCC 68 03(ctaA) and Synechocystis PCC 6803(pacS), Conversely, plastocyanin transcr ipts (petE) were less abundant in both mutants at this [copper]. Synechocys tis PCC 6803(ctaA) and Synechocystis PCC 6803(pacS) showed increased iron d ependence with impaired growth in deferoxamine mesylate (iron chelator)cont aining media. Double mutants also deficient in cytochrome c(6), Synechocyst is PCC 6803(petJ,ctaA) and Synechocystis PCC 6803(petJ,pacS), were viable, but the former had increased copper dependence with severely impaired growt h in the presence of bathocuproinedisulfonic acid (copper chelator), Analog ous transporters are likely to supply copper to plastocyanin in chloroplast s.