Gregor Grass

Escherichia coli mechanisms of copper homeostasis in a changing environment

Escherichia coli is equipped with multiple systems to ensure safe copper handling under varying environmental conditions. The Cu(I)-translocating P-type ATPase CopA, the central component in copper homeostasis, is responsible for removing excess Cu(I) from the cytoplasm. The multi-copper oxidase CueO and the multi-component copper transport system CusCFBA appear to safeguard the periplasmic space from copper-induced toxicity. Some strains of E. coli can survive in copper-rich environments that would normally overwhelm the chromosomally encoded copper homeostatic systems. Such strains possess additional plasmid-encoded genes that confer copper resistance. The pco determinant encodes genes that detoxify copper in the periplasm, although the mechanism is still unknown. Genes involved in copper homeostasis are regulated by MerR-like activators responsive to cytoplasmic Cu(I) or two-component systems sensing periplasmic Cu(I). Pathways of copper uptake and intracellular copper handling are still not identified in E. coli.

Crystal structure and electron transfer kinetics of CueO, a multicopper oxidase required for copper homeostasis in Escherichia coli

CueO (YacK), a multicopper oxidase, is part of the copper-regulatory cue operon in Escherichia coli. The crystal structure of CueO has been determined to 1.4-Å resolution by using multiple anomalous dispersion phasing and an automated building procedure that yielded a nearly complete model without manual intervention. This is the highest resolution multicopper oxidase structure yet determined and provides a particularly clear view of the four coppers at the catalytic center. The overall structure is similar to those of laccase and ascorbate oxidase, but contains an extra 42-residue insert in domain 3 that includes 14 methionines, nine of which lie in a helix that covers the entrance to the type I (T1, blue) copper site. The trinuclear copper cluster has a conformation not previously seen: the Cu-O-Cu binuclear species is nearly linear (Cu-O-Cu bond angle = 170°) and the third (type II) copper lies only 3.1 Å from the bridging oxygen. CueO activity was maximal at pH 6.5 and in the presence of >100 μM Cu(II). Measurements of intermolecular and intramolecular electron transfer with laser flash photolysis in the absence of Cu(II) show that, in addition to the normal reduction of the T1 copper, which occurs with a slow rate (k = 4 × 107 M−1⋅s−1), a second electron transfer process occurs to an unknown site, possibly the trinuclear cluster, with k = 9 × 107 M−1⋅s−1, followed by a slow intramolecular electron transfer to T1 copper (k ∼10 s−1). These results suggest the methionine-rich helix blocks access to the T1 site in the absence of excess copper.

The Pco proteins are involved in periplasmic copper handling in Escherichia coli.

The interactions between the plasmid-borne copper resistance determinant, pco, and the main copper export system in Escherichia coli have been investigated and no direct interaction has been found. The PcoE and PcoC proteins are periplasmic and PcoC binds one Cu ion per protein molecule. PcoA is also periplasmic and can substitute for the chromosomally encoded CueO protein. The pco determinant is proposed to exert its effect through periplasmic handling of excess copper ions and to increase the level of resistance to copper ions above that conferred by copA alone.

Biocidal Mechanisms of Metallic Copper Surfaces

Hospital acquired infections (HAI), also known as nosocomial infections, have a vast impact on patient and staff health and affect survival chances of patients with compromised immune system, elderly, and young children. Moreover, hospital environments are favoring the development of drug-resistant strains of bacteria, making treatment of such HAI more challenging. The Center of Disease Control estimates that one of the deadliest types of antibiotic-resistant bacteria, MRSA (methicillin-resistant Staphylococcus aureus), causes 19,000 death cases per year, whereas another superbug, Clostridium difficile, causes 500,000 incidents per year.