Environmental conditions? Nutrients… Oxygen… Temperature… …. ? ? ? ? ? ? ? ? ?

Two-component regulatory systems Include: 1- a histidine kinase (HK), or sensory kinase. Receives a signal and phosphorylates a histidine residue HK + ATP KH-P + ADP 2- a response regulator (RR). The RR is phosphorylated on an aspartate residue by HK-P RR + HK-P RR-P (active) + HK 3- a phosphatase, that can be the HK, the RR or another protein RR-P + H2O RR + Pi

MODEL OF HK ACTIVATION

OSMOREGULATION

Response to changes in osmolarity

PHOSPHATE AVAILABILITY

The PHO regulon

SENSING OXYGEN AVAILABILITY The Arc system (aerobic respiration control) Arc is responsible for: 1 – Repression, under anaerobiosis conditions, of genes encoding: TCA enzymes Glioxylate cycle enzymes Several dehydrogenases necessary for growth under aerobiosis (piruvate dehydrogenase) Enzymes involved in fatty acid oxidation Citochrome o oxidase 2 – Induction, under anaerobiosis, of genes encoding: Pyruvate formate lyase 3 – Induction, under low O2 concentrations, of gene encoding: Citochrome d oxidase, cobalamine and pyruvate formate lyase

The Arc system (aerobic respiration control)

Responses to changes in oxygen availabitiy The Fnr, SoxR, and ArcB are involved in oxygen sensing and regulation of metabolism Shift aerobic/anaerobic

A schematic representation of signal transduction by the Arc two-component system. Kwon O et al. J. Biol. Chem. 2003;278:13192-13195 ©2003 by American Society for Biochemistry and Molecular Biology

The FNR protein

The NarQ/NarP and NarX/NarL TCS are also involved in anerobic/anaerobic transitions

Oxidative stress response in E. coli

The heat shock response

HSP are chaperones or proteases