Identification Of LI1158 From Lawsonia Intracellularis As The Translocator

Lawsonia intracellularis,the causative agent of proliferative enteropathy(PPE),is an obligate intracellular Gram-negative bacterium.Analysis of L.intracellularis has revealed that its genome encodes a type III secretion system(T3SS)through which the pathogen delivers,in a single step,effector proteins into its human host cell cytosol to modulate host-cell functions and establish a unique intracellular niche for replication.The translocon proteins located at the top of the T3SS needle filament are essential for its function,as they form pores in the host-cell membrane.However,little is known about the L.intracellularis T3SS and translocon proteins.In this study,we analyzed the sequence of LI1158,identified the characteristics of T3S translocators and deduced that LI1158 is the putative major hydrophobic translocator of L.intracellularis.By using Yersinia pseudotuberculosis as a surrogate system,we found that the full-length LI1158 protein was expressed and secreted in a Ca2+dependent fashion and that the secretion signal was located at the N terminus of LI1158(aa 1-40).Furthermore,LI1158 was isolated in a fraction detached from the bacterial cell surface,indicating that this protein is partially assembled into complexes on the bacterial cell surface.Moreover,LI1158 exists as an oligomer and self-associates when expressed in yeast.Finally,we found that LI1158 exists as a monomer in mammalian cells and undergoes an unknown modification in mammals,as it does in yeast.Taken together,our data indicate that LI1158 is a putative T3S translocon protein of L.intracellularis.