The subunits of cholera toxin: structure, stoichiometry, and function

Area of Science:

• Microbiology
• Biochemistry

Background:

• Vibrio cholerae produces a toxin responsible for cholera.
• The toxin's structure and function are crucial for understanding its pathogenicity.

Purpose of the Study:

• To elucidate the subunit structure and functional roles of Vibrio cholerae toxin.
• To investigate the dissociation properties and molecular weights of toxin subunits.

Main Methods:

• Sedimentation equilibrium
• Gel chromatography
• Dodecylsulfate gel electrophoresis
• Cross-linking studies with methyl-4-mercaptobutyrimidate

Main Results:

• The cholera toxin exhibits an AB4 structure, with subunit A and a B-subunit aggregate (choleragenoid).
• Subunit A (27,000 daltons) consists of two disulfide-bonded polypeptide chains.
• Subunit B (14,000 daltons) mediates cell membrane binding, facilitating subunit A's interaction.

Conclusions:

• The AB4 structure is confirmed through cross-linking studies.
• Subunit B's primary role is cell binding, not direct interaction with adenylate cyclase.
• Subunit A possesses intrinsic activity, but its interaction is facilitated by subunit B.