Structural and functional studies of truncated hemolysin A from Proteus mirabilis

Area of Science:

• Microbiology
• Structural Biology
• Biochemistry

Background:

• Hemolysin A is part of the two-partner secretion pathway, a common mechanism in Gram-negative bacteria.
• The precise mechanism of action for two-partner hemolysins remains incompletely understood.
• Understanding hemolysin function is crucial for deciphering bacterial pathogenesis.

Purpose of the Study:

• To elucidate the structure and function of a truncated hemolysin A (HpmA265) from Proteus mirabilis.
• To investigate the mechanism of hemolysin A activation and hemolysis.
• To provide the first structural insights into a two-partner secretion pathway (TpsA) hemolysin.

Main Methods:

• Functional assays including hemolysis experiments.
• Structural determination using X-ray crystallography.
• Biophysical characterization using Circular Dichroism (CD) spectroscopy.
• Cellular localization studies with laser scanning confocal microscopy.

Main Results:

• Truncated HpmA265 demonstrated a unidirectional, cooperative, biphasic activity profile when initiating hemolysis.
• The first X-ray structure of a TpsA hemolysin revealed a right-handed parallel beta-helix with specific structural motifs (CXXC disulfide bond, solvent molecules, carboxyamide ladder).
• Mutating the CXXC motif reduced hemolysin activity and stability, while the structure showed a dry dimeric interface facilitating interactions.

Conclusions:

• A model for template-assisted hemolysis is proposed, involving cooperative beta-strand interactions between HpmA265 and full-length hemolysin A.
• The conserved CXXC motif plays a role in facilitating these interactions and stabilizing the protein structure.
• This work provides a mechanistic understanding of hemolysin A activation and function within the two-partner secretion system.