Multipart Chaperone-Effector Recognition in the Type III Secretion System of Chlamydia trachomatis

Area of Science:

• Microbiology
• Molecular Biology
• Structural Biology

Background:

• Chlamydia trachomatis utilizes effector protein secretion for virulence.
• The type III secretion (T3S) system is crucial for this process.
• Scc1 and Scc4 chaperones facilitate the secretion of CopN, an effector and plug protein, but the mechanism is unclear.

Purpose of the Study:

• To biochemically and structurally characterize the Scc1-Scc4-CopN interaction.
• To identify key residues involved in the Scc4-Scc1 interaction.
• To explore the link between T3S and bacterial transcriptional regulation.

Main Methods:

• Biochemistry
• Mass spectrometry
• Nuclear magnetic resonance (NMR) spectroscopy
• Genetic analyses (alanine substitutions)

Main Results:

• Scc4 complexes with Scc1 and CopN during the late developmental cycle of C. trachomatis.
• Scc4 and Scc1 exhibit dynamic interactions throughout the bacterial developmental cycle.
• Specific amino acid residues in Scc4 are critical for Scc4-Scc1 interaction and ternary complex formation.
• Scc4's role in transcription is confirmed, linking T3S to gene expression.

Conclusions:

• The Scc4·Scc1·CopN ternary complex formation is essential for effector secretion.
• The T3S process in C. trachomatis is intricately linked to bacterial transcriptional events.
• Scc4 acts as a central mediator, connecting T3S and gene expression regulation.