EstG is a novel esterase required for cell envelope integrity in Caulobacter

Area of Science:

• Microbiology
• Enzymology
• Bacterial Physiology

Background:

• Bacterial cell envelope regulation is vital for survival and a source of antibiotic targets.
• Understanding enzymes maintaining cell envelope homeostasis is crucial for developing new antimicrobials.

Purpose of the Study:

• To identify and characterize novel enzymes involved in bacterial cell envelope homeostasis.
• To investigate the function of the newly identified enzyme EstG in Caulobacter crescentus.

Main Methods:

• Genetic analysis linking EstG to OPG synthesis and hydrolysis pathways.
• Crystal structure determination of EstG.
• In vitro biochemical assays to determine EstG's enzymatic activity and substrate.
• Biochemical fractionation to identify EstG's substrate.

Main Results:

• EstG, despite structural similarities to cell wall enzymes, exhibits esterase activity, not on cell wall substrates.
• EstG acts on a novel cyclic hexamer of glucose, the first described OPG in Caulobacter.
• EstG, OpgH, and BglX form a previously unknown pathway for osmoregulated periplasmic glucans (OPGs).

Conclusions:

• EstG is a novel enzyme with esterase activity on cyclic OPGs, contributing to bacterial stress resistance.
• This discovery establishes a new class of OPGs and an associated regulatory pathway in Caulobacter.
• The EstG-mediated OPG pathway is important for bacterial adaptation and survival under stress conditions.