Assembly and Secretion of Oligomeric Toxins

Abstract

Pathogenic microorganisms produce a myriad of different virulence factors that range in complexity from polymers of simple disaccharides to multimeric protein toxins and adhesins. This structural and functional diversity belies a common biosynthetic requirement shared by all virulence factors: that they must cross the membrane of the bacterium in which they are produced before they can gain access to the host and express their pathogenic properties. The processes of membrane translocation result in either the complete secretion of a pathogenic molecule into the external milieu, eg. extracellular toxins, siderophores etc., or to their assembly onto the bacterial surface, as in the case of adhesins, pili, outer membrane porins, and carbohydrate capsules. In this paper we discuss the mechanisms of protein export and secretion in bacterial cells, and in particular the secretion of complex oligomeric toxins that are responsible for causing cholera and related diarrhoeal diseases.