# Systematic and synthetic biology insights into copper homeostasis in Escherichia coli

## TL;DR

The paper explores how Escherichia coli manages copper levels using two regulatory systems, revealing new details about their roles and interactions.

## Contribution

The study provides novel insights into the specific roles of the Cus system and the synergistic behavior of copper response systems in E. coli.

## Key findings

- The Cus system responds only to Cu+ and not Cu2+.
- CusS acts as both a kinase and phosphatase depending on Cu+ presence.
- Cue and Cus systems work synergistically in a concentration-dependent manner.

## Abstract

Copper serves as an essential trace element in biological systems through its association with metalloenzymes. Two major regulatory systems (cueR and cus) participate in the transcriptional regulation of copper homeostasis genes, yet critical mechanisms remain poorly understood. We systematically investigated E. coli’s copper response using systems and synthetic biology approaches, revealing more detailed mechanisms. Our results suggested that the cus system specifically responds to Cu+ but not Cu2+, with Cu2+ to Cu+ reduction occurring primarily in the cytoplasm. Cu+ in the periplasmic space mainly originates from CopA-mediated export through the cytoplasm. We discovered that CusR exhibits signal crosstalk, causing baseline expression, which can be regulated by optimal CusS concentrations. CusS functions as both a kinase and a phosphatase depending on Cu+ presence. We quantified E. coli’s response to various extracellular Cu2+ concentrations, ultimately clarifying the relationship between the two copper ion response systems. These findings provide comprehensive insights into bacterial copper homeostasis mechanisms.

•CueO mediates copper detoxification primarily via enzymatic oxidation rather than chelation•The Cus system is exclusively triggered by Cu+ and not Cu2+•CusS displays kinase and phosphatase activities regulated by Cu+•The Cue and Cus systems operate in a concentration-dependent synergistic manner

CueO mediates copper detoxification primarily via enzymatic oxidation rather than chelation

The Cus system is exclusively triggered by Cu+ and not Cu2+

CusS displays kinase and phosphatase activities regulated by Cu+

The Cue and Cus systems operate in a concentration-dependent synergistic manner

Biological sciences; Medical Microbiology; Microbial metabolism; Microbial physiology; Molecular microbiology