ABSTRACT
A. Cholera 124 B. Enterotoxinogenic E. coli 126 c. Other Enteropathogens 127
III. CHOLERA TOXIN AND RELATED ENTEROTOXINS 127 A. Toxin Structure 127 B. Toxin Action 133
IV. TOXIN GENE ORGANIZATION 135 A. The ctx Genes Encoding Cholera Toxin 135 B. The etx Genes Encoding E. coli Heat-Labile Enterotoxin 137 C. Operon Structure 137
v. BIOGENESIS OF CHOLERA TOXIN AND RELATED ENTEROTOXINS 138 A. Regulation of Toxin Expression 138 B. Translational Control of Subunit Stoichiometry 142 c. Toxin Export Across the Cytoplasmic Membrane 144 D. Toxin Folding and Assembly 151 E. Toxin Secretion Across the Outer Membrane 162
VI. CONCLUDING REMARKS 171 REFERENCES 171
124 Hirst
Virtually all of the classical virulence factors produced by pathogenic microorganisms, such as surface-associated adhesins, capsular polysaccharides, lipopolysaccharides, siderophores, and toxins, are secreted molecules. Thus, they must undergo a process of translocation from their site of synthesis (usually in the cytoplasm or on the cytoplasmic membrane), through the microbial envelope to a location where they can exhibit their functional virulence properties. Incorporation of virulence factors in the microbial cell surface or their secretion into the surrounding milieu depends on multiple cellular processes, which include the events of macromolecular synthesis, translocation, processing, modification, folding, assembly, and secretion or integration. A term that usefully encompasses such a wide range of events is macromolecular biogenesis.
