Molecular mechanisms of copper resistance and accumulation in bacteria

Abstract

An unusual mechanism of metal resistance is found in certain plant pathogenic strains of Pseudomonas syringae that are exposed to high levels of copper compounds used in disease control on agricultural crops. These bacteria accumulate blue Cu2+ ions in the periplasm and outer membrane. At least part of this copper sequestering activity is determined by copper-binding protein products of the copper resistance operon (cop). Potential copper-binding sites of the periplasmic CopA protein show conservation with type-1, type-2, and type-3 copper sites of several eukaryotic multi-copper oxidases. In addition to compartmentalization of copper in the periplasm, two components of the cop operon, copC and copD, appear to function in copper uptake into the cytoplasm. Copper resistance operons related to cop have been described in the related plant pathogen Xanthomonas campestris and in Escherichia coli, but these resistance systems may differ functionally from the Pseudomonas syringae system.

PcoE — A metal sponge expressed to the periplasm of copper resistance Escherichia coli. Implication of its function role in copper resistance

“…Homologous copper-resistance cop determinants copABCDRS have been found in copper resistant strains of Pseudomonas syringae pathovar tomato isolated from plants exposed to high levels of copper compounds and in strains of Ralstonia metallidurans isolated from sediments of a zinc decantation basin in Belgium [10,14]. The operon structures of these cop gene cluster are similar to their pco counterparts, as are the protein sequences, suggesting a conserved mechanism of copper resistance.…”

“…Some bacteria can survive environmental concentrations of copper in the millimolar concentration range by expressing plasmid-encoded resistance operons [9][10][11][12][13][14]. The plasmid pRJ1004 of E. coli carries a copper resistance pco gene cluster that features seven pco genes pcoABCDRSE, arranged in two operons, pcoABCD and pcoRS, plus a separate pcoE gene.…”

Structural Biology of Copper Trafficking

“…A homologous copper resistance gene cluster, the copABCDRS operon, has been identified in several plant pathogens ( P. syringae and Xanthomonas campestris ) 64. Cells expressing the cop cluster accumulate and sequester copper in the periplasm causing the cells to turn blue in color 64,153. CopC is the PcoC homologue and has also been structurally characterized (Table 1).…”

Crystal structure and dimerization equilibria of PcoC, a methionine-rich copper resistance protein from Escherichia coli

“…Although the gene products are homologous, the two systems are postulated to function in different manners [13]. The cop proteins can sequester copper in the periplasm and outer membranes to such high levels that the resistant bacterial colonies are blue [14,15]. By contrast, bacteria with the pco determinant show no significant copper accumulation and do not become blue upon copper exposure [16], but do exhibit enhanced copper export [17].…”