A peptide signal for adapter protein-mediated degradation by the AAA+ protease ClpCP

Area of Science:

• Molecular biology
• Microbial genetics

Background:

• ComS is an antiadaptor protein that interacts with MecA.
• This interaction displaces ComK, a competence transcription factor, from MecA.
• ComK displacement by ComS protects ComK from ClpCP protease-mediated degradation, initiating bistable gene expression.

Purpose of the Study:

• Identify the specific motifs on ComK and ComS responsible for MecA binding.
• Characterize the mechanism by which ComS binding to MecA affects ComK stability.
• Elucidate the role of ComS-MecA interaction in regulating competence gene expression.

Main Methods:

• Peptide synthesis and binding assays to determine protein-protein interactions.
• In vivo degradation assays using a green fluorescent protein reporter system.
• Crosslinking and competition experiments to map binding sites on MecA.

Main Results:

• Identified conserved binding motifs (FMLYPK in ComK, IILYPR in ComS) near the termini of both proteins.
• A 17-residue peptide from ComK containing the motif exhibited similar MecA binding affinity as full-length ComK.
• Peptides containing the motif were sufficient to induce degradation of a reporter protein in vivo.
• Competition and crosslinking studies confirmed that ComK and ComS peptides bind to the same site on MecA.

Conclusions:

• ComS functions as an antiadaptor by directly competing with ComK for binding to MecA.
• This competitive binding mechanism protects ComK from degradation, thereby regulating bistable gene expression.
• The identified conserved motifs are crucial for the antiadaptor function of ComS and the regulation of competence in bacteria.