title: Identification of a specific chaperone for SptP, a substrate of the centisome 63 type III secretion system of Salmonella typhimurium.
abstract: Salmonella typhimurium uses of a type III protein secretion system encoded at centisome 63 of its chromosome to deliver effector molecule into the host cell. These proteins stimulate host cell responses such as reorganization of the actin cytoskeleton and activation of transcription factors. One of these effector proteins is SptP, a tyrosine phosphatase that causes disruption of the host cell actin cytoskeleton. A characteristic feature of many substrates of type III secretion systems is their association with specific cytoplasmic chaperones which appears to be required for secretion and/or translocation of these proteins into the host cell. We report here the identification of SicP, a 13-kDa acidic polypeptide that is encoded immediately upstream of sptP. A loss-of-function mutation in sicP resulted in drastically reduced levels of SptP but did not affect sptP expression, indicating that SicP exerts its effect posttranscriptionally. Pulse-chase experiments demonstrated that the loss of SicP leads to increased degradation of SptP. In addition, we show that SicP binds to SptP directly and that the binding site is located between residues 15 and 100 of the tyrosine phosphatase. Taken together, these results indicate that SicP acts as a specific chaperone for SptP.
authors.affiliation: Department of Molecular Genetics and Microbiology, School of Medicine, State University of New York at Stony Brook 11794-5222, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Fu
authors.forename: J E
authors.initials: JE
authors.lastname: Galán
mesh_terms: D000199:Actins / Q000378:metabolism; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D002876:Chromosomes, Bacterial; D003001:Cloning, Molecular; D003169:Complement Inactivator Proteins / Q000235:genetics; D003599:Cytoskeleton / Q000502:physiology; D007700:Kinetics; D008969:Molecular Sequence Data; D010957:Plasmids; D016133:Polymerase Chain Reaction; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000737:chemistry; D012486:Salmonella typhimurium / Q000235:genetics* / Q000378:metabolism*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D000199:Actins; D001426:Bacterial Proteins; D003169:Complement Inactivator Proteins; D011993:Recombinant Fusion Proteins; C097739:SIC protein, Streptococcus; D017027:Protein Tyrosine Phosphatases