title: VirB1, a component of the T-complex transfer machinery of Agrobacterium tumefaciens, is processed to a C-terminal secreted product, VirB1.
abstract: During genetic transformation of plant cells by Agrobacterium tumefaciens, 11 VirB proteins and VirD4 are proposed to form a transmembrane bridge to transfer a DNA-protein complex (T-complex) into the plant cytoplasm. In this study, the localization of the first product of the virB operon, VirB1, was studied in detail. While full-length VirB1 localized mostly to the inner membrane, an immunoreactive VirB1 product was found as soluble processed form, designated VirB1*. Equal amounts of VirB1* could be detected in concentrated culture supernatants versus associated with the cell. VirB1* was purified from the supernatant of vir-induced cells by ammonium sulfate precipitation and Q-Sepharose chromatography. Sequence analysis of the N terminus of VirB1* localized the processing site after amino acid 172 of VirB1. Cell-associated VirB1* was partly removed by vortexing, suggesting a loose association with the cell or active secretion. However, cross-linking and coimmunoprecipitation showed a close association of cell-bound VirB1* with the VirB9-VirB7 heterodimer, a membrane-associated component of the T-complex transfer machinery. Homologies of the N-terminal part of VirB1 to bacterial transglycosylases suggest that it may assist T-complex transfer by local lysis of the bacterial cell wall, whereas the exposed localization of the C-terminal processing product VirB1* predicts direct interaction with the plant. Thus, VirB1 may be a bifunctional protein where both parts have different functions in T-complex transfer from Agrobacterium to plant cells.
authors.affiliation: Department of Plant and Microbial Biology, University of California at Berkeley, 94720, USA.
authors.forename: C
authors.initials: C
authors.lastname: Baron
authors.forename: M
authors.initials: M
authors.lastname: Llosa
authors.forename: S
authors.initials: S
authors.lastname: Zhou
authors.forename: P C
authors.initials: PC
authors.lastname: Zambryski
mesh_terms: D016960:Agrobacterium tumefaciens / Q000378:metabolism* / Q000472:pathogenicity; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004269:DNA, Bacterial / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D011499:Protein Processing, Post-Translational; D012995:Solubility; D014774:Virulence; D037521:Virulence Factors
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; C036483:T-DNA; D037521:Virulence Factors