Structural insights into pre-pore intermediates of alpha-hemolysin in the lipidic environment

Area of Science:

• Microbiology
• Structural Biology
• Biophysics

Background:

• Staphylococcus aureus secretes pore-forming toxins (PFTs) that damage host cell membranes during infection.
• The structural basis of PFT interaction with host cell membranes remains poorly understood.
• No prior studies have elucidated the intermediate or pore structures of PFTs within a biomembrane context.

Purpose of the Study:

• To investigate the structural mechanisms of alpha-hemolysin (α-HL), a beta-PFT, in various lipidic environments.
• To explore the role of membrane composition and properties in α-HL pore formation.
• To elucidate the structure-function relationship of the α-HL pre-pore to pore transition.

Main Methods:

• Single-particle cryo-electron microscopy (cryo-EM) to determine toxin structures.
• Single-molecule and confocal imaging to study lipid destabilization.
• Mutational studies to validate lipid-protein interactions.

Main Results:

• Eight cryo-EM structures of wildtype α-HL were resolved with different liposome compositions (varying lipid chain lengths and components like cholesterol and sphingomyelin).
• Lipid chain length and membrane composition influence the formation of α-HL intermediate pre-pores and complete pores.
• Sphingomyelin-induced membrane rigidity significantly increases the population of α-HL pre-pore states.

Conclusions:

• This study provides novel structural insights into the α-HL pre-pore to pore transition within a lipidic environment.
• Membrane properties critically modulate the conformational states and pore-forming activity of α-HL.
• Findings advance the understanding of PFT-membrane interactions and their role in bacterial pathogenesis.