Secretion Systems of Pathogenic Escherichia coli

Abstract

Protein secretion plays a central role in modulating the interactions ofbacteria with their environments. Bacterial ribosomes synthesize up to 8000 different proteins. Almost half of these become integrated in membranes and are secreted to the periplasm or to the external milieu. Many bacterial processes , such as DNA replication, motility, transport, antibiotic resistance, scavenging of chemicals, and pathogenesis, depend on protein secretion. Thereby, evolutionarily unrelated protein nanomachines have been developed, which allow exported proteins to cross the Gram-negative membranes. Bacterial proteins can be exported directly from the cytoplasm out of the cell by a one-step (cytoplasm to extracellular milieu), including the type I secretion system (T1SS), T3SS, T4SS, and T6SS, or two-step (periplasm translocation step), including the T2SS and T5SS, while the T4SS can use either the one- or two-step mechanism. The T3SS, T5SS, and T6SS are the more common secretion systems in Escherichia coli and most of the secreted substrates are virulence factors related topathogenic E. coli . In this chapter, we will describe the main characteristic of these last three secretion systems.