Crystal structure of secretory protein Hcp3 from Pseudomonas aeruginosa

Area of Science:

• Microbiology
• Structural Biology
• Bacterial Pathogenesis

Background:

• The Type VI secretion system (T6SS) is a critical mechanism for protein transport across the cell envelope in Gram-negative bacteria.
• Pseudomonas aeruginosa utilizes T6SS for exporting effector proteins essential for its virulence and pathogenesis in humans.
• The HSI-I locus in P. aeruginosa encodes proteins involved in T6SS, including Hcp1, known to form hexameric rings and nanotubes.

Purpose of the Study:

• To elucidate the structure of the Hcp3 protein, a paralogue of Hcp1, from Pseudomonas aeruginosa.
• To compare the structural assembly and organization of Hcp3 with its known paralogue, Hcp1.

Main Methods:

• Protein structure determination of Hcp3 from P. aeruginosa.
• Comparative structural analysis of Hcp3 monomers and hexamers against Hcp1.

Main Results:

• The Hcp3 monomer shares structural resemblance to Hcp1, despite low amino acid sequence similarity.
• Hcp3 monomers assemble into hexameric rings, analogous to Hcp1.
• Unlike Hcp1's head-to-tail nanotube formation, Hcp3 rings stack in a head-to-head manner, creating distinct double-ring structures.

Conclusions:

• Hcp3 exhibits a unique ring-stacking mechanism within the Type VI secretion pathway.
• The head-to-head double-ring structure of Hcp3 represents a novel assembly mode compared to Hcp1 nanotubes.
• These structural findings provide insights into the functional diversity of Hcp paralogues in P. aeruginosa pathogenesis.