title: EscC is a chaperone for the Edwardsiella tarda type III secretion system putative translocon components EseB and EseD.
abstract: Edwardsiella tarda is a Gram-negative enteric pathogen that causes disease in both humans and animals. Recently, a type III secretion system (T3SS) has been found to contribute to Ed. tarda pathogenesis. EseB, EseC and EseD were shown to be secreted by the T3SS and to be the major components of the extracellular proteins (ECPs). Based on sequence similarity, they have been proposed to function as the 'translocon' of the T3SS needle structure. In this study, it was shown that EseB, EseC and EseD formed a protein complex after secretion, which is consistent with their possible roles as translocon components. The secretion of EseB and EseD was dependent on EscC (previously named Orf2). EscC has the characteristics of a chaperone; it is a small protein (13 kDa), located next to the translocators in the T3SS gene cluster, and has a coiled-coil structure at the N-terminal region as predicted by coils. An in-frame deletion of escC abolished the secretion of EseB and EseD, and complementation of DeltaescC restored the export of EseB and EseD into the culture supernatant. Further studies showed that EscC is not a secreted protein and is located on the membrane and in the cytoplasm. Mutation of escC did not affect the transcription of eseB but reduced the amount of EseB as measured by using an EseB-LacZ fusion protein in Ed. tarda. Co-purification studies demonstrated that EscC formed complexes with EseB and EseD. The results suggest that EscC functions as a T3SS chaperone for the putative translocon components EseB and EseD in Ed. tarda.
authors.affiliation: Department of Biological Sciences, Faculty of Science, National University of Singapore, 117543, Singapore.
authors.forename: Jun
authors.initials: J
authors.lastname: Zheng
authors.affiliation: Department of Biological Sciences, Faculty of Science, National University of Singapore, 117543, Singapore.
authors.forename: Nan
authors.initials: N
authors.lastname: Li
authors.affiliation: Department of Biological Sciences, Faculty of Science, National University of Singapore, 117543, Singapore.
authors.forename: Yuen Peng
authors.initials: YP
authors.lastname: Tan
authors.affiliation: Department of Biological Sciences, Faculty of Science, National University of Singapore, 117543, Singapore.
authors.forename: J
authors.initials: J
authors.lastname: Sivaraman
authors.affiliation: Department of Biological Sciences, Faculty of Science, National University of Singapore, 117543, Singapore.
authors.forename: Yu-Keung
authors.initials: YK
authors.lastname: Mok
authors.affiliation: Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China.
authors.forename: Zhao Lan
authors.initials: ZL
authors.lastname: Mo
authors.affiliation: Department of Biological Sciences, Faculty of Science, National University of Singapore, 117543, Singapore.
authors.forename: Ka Yin
authors.initials: KY
authors.lastname: Leung
mesh_terms: D000818:Animals; D019677:Artificial Gene Fusion; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000737:chemistry; D003593:Cytoplasm / Q000378:metabolism; D020609:Edwardsiella tarda / Q000378:metabolism* / Q000472:pathogenicity; D004756:Enterobacteriaceae Infections / Q000382:microbiology; D005393:Fish Diseases / Q000382:microbiology; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D017930:Genes, Reporter; D018832:Molecular Chaperones / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D046912:Multiprotein Complexes; D016254:Mutagenesis, Insertional; D011485:Protein Binding; D011487:Protein Conformation; D021381:Protein Transport; D014158:Transcription, Genetic; D037521:Virulence Factors / Q000737:chemistry / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D018832:Molecular Chaperones; D046912:Multiprotein Complexes; D037521:Virulence Factors