Comparison of the Structure, Regulation and Functions between Type Three and Type Six Secretion System in Gram-Negative Bacteria

Sara Badr,Kangmin Duan,Yanqi Li

doi:10.4172/2161-0703.1000243

Abstract

Bacteria have evolved multiple protein secretion systems to survive and cope with surrounding environmental stresses. So far, there are seven secretion systems (type I to type VII), which have been identified and demonstrated the structural and molecular mechanisms. Among them, type three secretion system (T3SS), hallmark of acute infection, is considered as the most complicated system and can translocate effector proteins directly into host cell through a needle-like apparatus. Type six secretion system (T6SS) targets both prokaryotic and eukaryotic cells using a bacteriophage-like structure and plays a role in pathogenesis and bacterial competition. This review is based on our understanding of comparison of the structure, regulation, function and application between T3SS and T6SS. Understanding the structural and functional mechanisms, as well as the difference and relationship between these two secretion systems will help our understanding of bacterial pathogenesis and interspecies interaction.

Highlights

Secretion systems have been developed by pathogens for the purpose of survival in host environments, competition, colonization, and infection
Marsden et al discovered that virulence factor regulator (Vfr) can regulate expression of the Pseudomonas aeruginosa type III secretion system, by directly activating exsA transcription [24]
Bacteria delivers a series of effector proteins via different secretion systems to provide a fitness advantage in survival and competing for resources

Summary

Introduction

Secretion systems have been developed by pathogens for the purpose of survival in host environments, competition, colonization, and infection. It injects effector proteins directly into the cytoplasm of target host cells, to evade immune system and facilitate bacterial survival or to inhibit cellular function. T6SS is one of the secretion systems recognized recently in 2006 in Pseudomonas aeruginosa and Vibrio cholerae It is a one-step secretion system and it functions as a defense mechanism against other bacteria (antibacterial activity) in a polymicrobial environment. Permeabilization pore forming proteins PopD and PopB are hydrophobic translocator proteins, which function in host cells under acidic conditions (PH) Until this day, researchers are debating on the exact mechanism controlling needle length dimensions, and substrate switching. Serum bactericidal assay was implemented and confirmed the efficiency of antibodies against VipA \VipB This application demonstrated the ability of T6SS sheaths to integrate various proteins in one nanoparticle, that can be transmitted on one antigen presenting cell (Figure 1)

Function and Applications

Conclusion and Future Prospects