title: An IcmF family protein, ImpLM, is an integral inner membrane protein interacting with ImpKL, and its walker a motif is required for type VI secretion system-mediated Hcp secretion in Agrobacterium tumefaciens.
abstract: An intracellular multiplication F (IcmF) family protein is a conserved component of a newly identified type VI secretion system (T6SS) encoded in many animal and plant-associated Proteobacteria. We have previously identified ImpL(M), an IcmF family protein that is required for the secretion of the T6SS substrate hemolysin-coregulated protein (Hcp) from the plant-pathogenic bacterium Agrobacterium tumefaciens. In this study, we characterized the topology of ImpL(M) and the importance of its nucleotide-binding Walker A motif involved in Hcp secretion from A. tumefaciens. A combination of beta-lactamase-green fluorescent protein fusion and biochemical fractionation analyses revealed that ImpL(M) is an integral polytopic inner membrane protein comprising three transmembrane domains bordered by an N-terminal domain facing the cytoplasm and a C-terminal domain exposed to the periplasm. impL(M) mutants with substitutions or deletions in the Walker A motif failed to complement the impL(M) deletion mutant for Hcp secretion, which provided evidence that ImpL(M) may bind and/or hydrolyze nucleoside triphosphates to mediate T6SS machine assembly and/or substrate secretion. Protein-protein interaction and protein stability analyses indicated that there is a physical interaction between ImpL(M) and another essential T6SS component, ImpK(L). Topology and biochemical fractionation analyses suggested that ImpK(L) is an integral bitopic inner membrane protein with an N-terminal domain facing the cytoplasm and a C-terminal OmpA-like domain exposed to the periplasm. Further comprehensive yeast two-hybrid assays dissecting ImpL(M)-ImpK(L) interaction domains suggested that ImpL(M) interacts with ImpK(L) via the N-terminal cytoplasmic domains of the proteins. In conclusion, ImpL(M) interacts with ImpK(L), and its Walker A motif is required for its function in mediation of Hcp secretion from A. tumefaciens.
authors.affiliation: Institute of Plant and Microbial Biology, Academia Sinica, Taipei, Taiwan.
authors.forename: Lay-Sun
authors.initials: LS
authors.lastname: Ma
authors.forename: Jer-Sheng
authors.initials: JS
authors.lastname: Lin
authors.forename: Erh-Min
authors.initials: EM
authors.lastname: Lai
mesh_terms: D016960:Agrobacterium tumefaciens / Q000235:genetics / Q000378:metabolism*; D020816:Amino Acid Motifs; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D017353:Gene Deletion; D005816:Genetic Complementation Test; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D015151:Immunoblotting; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism*; D020798:Two-Hybrid System Techniques; D001618:beta-Lactamases / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D008565:Membrane Proteins; D011994:Recombinant Proteins; D049452:Green Fluorescent Proteins; D001618:beta-Lactamases