Characterization of the multimeric Eps complex required for cholera toxin secretion

Vibrio cholerae causes diarrheal disease through colonization of the small intestine. A critical aspect of V. cholerae pathogenesis is its ability to actively secrete cholera toxin to the extracellular environment. This occurs via the type II secretion pathway, where the toxin subunits are first transported to the periplasm through the Sec pathway. Following folding and assembly the toxin is then translocated across the outer membrane by a specialized Extracellular Protein Secretion (Eps) machinery encoded by at least 13 genes. Although the Eps proteins are believed to form a secretion apparatus that spans both membranes, cholera toxin is thought to engage this complex first in the periplasm. In order to determine the organization of the Eps apparatus and to understand the mechanism of secretion, the Eps apparatus has been dissected and three of the components, EpsE, EpsL and EpsM, have been purified and characterized. They were shown to form a stable, multiprotein complex spanning the cytoplasmic membrane.