title: Tandem translation generates a chaperone for the Salmonella type III secretion system protein SsaQ.
abstract: Type III secretion systems (T3SSs) of bacterial pathogens involve the assembly of a surface-localized needle complex, through which translocon proteins are secreted to form a pore in the eukaryotic cell membrane. This enables the transfer of effector proteins from the bacterial cytoplasm to the host cell. A structure known as the C-ring is thought to have a crucial role in secretion by acting as a cytoplasmic sorting platform at the base of the T3SS. Here, we studied SsaQ, an FliN-like putative C-ring protein of the Salmonella pathogenicity island 2 (SPI-2)-encoded T3SS. ssaQ produces two proteins by tandem translation: a long form (SsaQ(L)) composed of 322 amino acids and a shorter protein (SsaQ(S)) comprising the C-terminal 106 residues of SsaQ(L). SsaQ(L) is essential for SPI-2 T3SS function. Loss of SsaQ(S) impairs the function of the T3SS both ex vivo and in vivo. SsaQ(S) binds to its corresponding region within SsaQ(L) and stabilizes the larger protein. Therefore, SsaQ(L) function is optimized by a novel chaperone-like protein, produced by tandem translation from its own mRNA species.
authors: Section of Microbiology, Centre for Molecular Microbiology and Infection, Imperial College London, London SW7 2AZ, United Kingdom.
authors: Xiu-Jun
authors: XJ
authors: Yu
authors: Section of Microbiology, Centre for Molecular Microbiology and Infection, Imperial College London, London SW7 2AZ, United Kingdom.
authors: Mei
authors: M
authors: Liu
authors: Division of Molecular Biosciences, Centre for Structural Biology, Imperial College London, London SW7 2AZ, United Kingdom.
authors: Steve
authors: S
authors: Matthews
authors: Section of Microbiology, Centre for Molecular Microbiology and Infection, Imperial College London, London SW7 2AZ, United Kingdom. Electronic address: d.holden@imperial.ac.uk.
authors: David W
authors: DW
authors: Holden
mesh_terms: D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics; D058947:Bacterial Secretion Systems / Q000502:physiology*; D018832:Molecular Chaperones / Q000096:biosynthesis* / Q000235:genetics; D014176:Protein Biosynthesis / Q000502:physiology*; D021381:Protein Transport / Q000502:physiology; D012486:Salmonella typhimurium / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D058947:Bacterial Secretion Systems; D018832:Molecular Chaperones