Type i secretion system – It takes three and a substrate

Abstract

Type I secretion systems are wide-spread in Gram-negative bacteria and mediate the one step translocation of a large variety of proteins serving for diverse purposes, including nutrient-acquisition or bacterial virulence. Common to most substrates of Type I secretion systems is the presence of a C-terminal secretion sequence that is not cleaved during or after translocation. Furthermore, these protein secretion nanomachineries are always composed of an ABC transporter, a membrane fusion protein, both located in the inner bacterial membrane, and a protein of the outer membrane. These three membrane proteins transiently form a 'tunnel-channel' across the periplasmic space in the presence of the substrate. Here we summarize the recent findings with respect to structure, function and application of Type I secretion systems.