Dimer recognition and secretion by the ESX secretion system in Bacillus subtilis

Area of Science:

• Microbiology
• Molecular Biology
• Protein Secretion

Background:

• Protein secretion typically involves unfolded polypeptides or monomeric proteins.
• The early secretory antigen 6 kDa (ESX) secretion system is crucial in various bacteria.

Purpose of the Study:

• To investigate a novel mechanism of protein secretion involving multimeric complexes.
• To identify the specific motifs and requirements for the secretion of a Bacillus subtilis ESX substrate.

Main Methods:

• Systematic mutagenesis of the ESX secretion substrate.
• Construction and analysis of mixed dimers.
• Targeted crosslinking experiments.

Main Results:

• Export of the substrate requires two independent motifs.
• These motifs form a composite secretion signal, with each motif contributed by a different subunit of the dimer.
• The dimer is likely secreted as a single unit.

Conclusions:

• Demonstrates the first experimental evidence for secretion of an intact multimeric complex via a composite signal.
• Highlights implications for protein biogenesis and quality control in secretion pathways.
• Suggests conservation of this mechanism across different ESX systems.