Cholesterol-binding cytolytic protein toxins

Area of Science:

• Microbiology
• Biochemistry
• Structural Biology

Background:

• Cholesterol-binding cytolysins (CBCs) are a diverse family of bacterial toxins.
• These toxins are produced by various Gram-positive bacteria and are lethal and lytic to eukaryotic cells.
• Their activity is dependent on membrane cholesterol and sulfhydryl groups.

Purpose of the Study:

• To investigate the structure-activity relationships of cholesterol-binding cytolysins.
• To identify key molecular determinants responsible for toxin binding to cholesterol and lytic activity.
• To understand the mechanism of pore formation in eukaryotic cell membranes.

Main Methods:

• Sequence analysis of cloned toxin genes.
• Site-directed mutagenesis of conserved residues, particularly cysteine and tryptophan.
• Elucidation of the 3-D structure of perfringolysin O.
• Biochemical assays to assess lytic activity and cholesterol binding.

Main Results:

• CBCs exhibit sequence homology, especially in the C-terminal region, with a conserved consensus sequence.
• A specific tryptophan residue in the conserved undecapeptide was found to be critical for lytic activity.
• The 3-D structure of perfringolysin O revealed four domains, with domain 4 mediating membrane interaction and a Trp-rich region adapting to cholesterol.
• Oligomerization involves multiple sites, leading to pore formation.

Conclusions:

• Cholesterol is the primary binding site for CBCs on eukaryotic cell membranes.
• Specific residues, particularly tryptophan, and structural domains are crucial for the lytic function of CBCs.
• The mechanism involves monomer binding, oligomerization, and pore formation, with conformational changes driven by cholesterol interaction.