Multicopper oxidases (MCOs) catalyze the oxidation of a variety of substrates while reducing oxygen into water through four copper atoms. As an additional feature, some MCOs display an enhanced activity in solution in the presence of Cu 2+. This is the case of the hyperthermophilic laccase HB27 from Thermus thermophilus, the physiologic role of which is unknown. As a particular feature, this enzyme presents a methionine rich domain proposed to be involved in copper interaction. In this work, laccase from T. thermophilus was produced in E. coli, and the effect of Cu 2+ on its electroactivity at carbon nanotube modified electrodes was investigated. Direct O2 electroreduction is strongly dictated by carbon nanotube surface chemistry in accordance with the enzyme dipole moment. In the presence of Cu 2+ , an additional low potential cathodic wave occurs, which was never described earlier. Analysis of this wave as a function 2 of Cu 2+ availability allows us to attribute this wave to a cuprous oxidase activity displayed by the laccase and induced by copper binding close to the Cu T1 center. A mutant lacking the methionine-rich hairpin domain characteristic of this laccase conserves its copper activity suggesting a different site of copper binding. This study provides new insight into the copper effect in methionine rich MCOs, and highlights the utility of the electrochemical method to investigate cuprous oxidase activity and to understand the physiological role of these MCOs.

With the increase of antibiotic drug resistance, alternative antibacterial treatment strategies are needed. Copper is a well-known antimicrobial and antiviral agent; however, the underlying molecular mechanisms by which copper causes cell death are not yet fully understood.

Bacteria possess the ability to adapt to changing environments. To enable this, cells use reversible post-translational modifications on key proteins to modulate their behavior, metabolism, defense mechanisms and adaptation of bacteria to stress. In this review, we focus on bacterial protein switches that are activated during exposure to oxidative stress. Such protein switches are triggered by either exogenous reactive oxygen species (ROS) or endogenous ROS generated as by-products of the aerobic lifestyle. Both thiol switches and metal centers have been shown to be the primary targets of ROS. Cells take advantage of such reactivity to use these reactive sites as redox sensors to detect and combat oxidative stress conditions. This in turn may induce expression of genes involved in antioxidant strategies and thus protect the proteome against stress conditions. We further describe the well-characterized mechanism of selected proteins that are regulated by redox switches. We highlight the diversity of mechanisms and functions (as well as common features) across different switches, while also presenting integrative methodologies used in discovering new members of this family. Finally, we point to future challenges in this field, both in uncovering new types of switches, as well as defining novel additional functions.