Membrane-bound enterotoxin of Vibrio cholerae

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• The transport mechanism of the complex cholera toxin molecule across Vibrio cholerae membranes is unknown.
• Cholera toxin is a large molecule (mol. wt 84000) composed of multiple subunits.

Purpose of the Study:

• To investigate the potential transport form of cholera toxin subunits across Vibrio cholerae membranes.
• To identify peptides associated with toxin transport under different growth conditions.

Main Methods:

• Culturing Vibrio cholerae under aerobic and anaerobic conditions at 37°C.
• Analyzing peptides in isolated inner and outer membranes using molecular weight determination.
• Treating membranes with sodium deoxycholate and trypsin to assess peptide release.
• Comparing membrane-bound peptides with subunits of purified cholera toxin.

Main Results:

• Two peptides (approx. mol. wt 22000 and 6000) were found in the inner and outer membranes of aerobically grown V. cholerae, but not in anaerobically grown cells.
• Sodium deoxycholate and trypsin released these 22000 and 6000 mol. wt peptides.
• Purified cholera toxin contains peptides of mol. wt 21000 (A1), 11000 (B subunit), and 5000 (A2).

Conclusions:

• The identified membrane peptides may represent the form in which cholera toxin subunits are transported across V. cholerae membranes.
• These peptides are postulated to be precursors of the A subunit of the cholera toxin molecule.