Structural basis of peptide secretion for Quorum sensing by ComA

Area of Science:

• Microbiology
• Structural Biology
• Biochemistry

Background:

• Quorum sensing (QS) regulates bacterial communication and is a target for combating antimicrobial resistance.
• ComA, a Gram-positive bacterial efflux pump, is vital for secreting competence-stimulating peptide (CSP) but its structure and function are poorly understood.

Purpose of the Study:

• To functionally characterize ComA as an ABC transporter.
• To determine the cryo-electron microscopy (cryo-EM) structures of ComA.
• To elucidate the molecular mechanism of CSP secretion by ComA.

Main Methods:

• Functional characterization of ComA as an ATP-binding cassette (ABC) transporter.
• Determination of ComA structures using cryo-electron microscopy (cryo-EM) in various states.
• In vitro peptidase activity assays and in vivo CSP export experiments.

Main Results:

• ComA exhibits high ATP affinity and a unique intracellular gate with electrostatic interactions.
• A binding pocket for two CSP molecules was identified, with negatively charged residues facilitating translocation.
• ATP-Mg2+, not ATP alone, induces the outward-facing conformation for CSP release.
• Mutations in key residues impaired ComA's peptidase activity and CSP export.

Conclusions:

• ComA functions as an ABC transporter mediating QS signal peptide secretion.
• Structural and functional insights into ComA provide potential targets for novel anti-QS drugs.
• This research advances understanding of bacterial communication and antimicrobial strategies.