title: The Gene Transfer Agent RcGTA Contains Head Spikes Needed for Binding to the Rhodobacter capsulatus Polysaccharide Cell Capsule.
abstract: Viruses and bacteriophages recognize cell surface proteins using receptor-binding proteins. In most tailed bacteriophages, receptor-binding proteins are located on the bacteriophage tail. The gene transfer agent of Rhodobacter capsulatus, RcGTA, morphologically resembles a tailed bacteriophage and binds to a capsular polysaccharide covering R. capsulatus cells. Here, we report that the RcGTA capsid (head) is decorated by spikes that are needed for binding to the capsule. The triangular spikes measured ~12nm and appeared to be attached at the capsid vertices. Head spike production required the putative carbohydrate-binding protein ghsB (rcc01080) previously thought to encode a side tail fiber protein. We found that ghsB is likely co-transcribed with ghsA (rcc01079) and that ghsA/ghsB is regulated by the CckA-ChpT-CtrA phosphorelay homologues and a quorum-sensing system. GhsA and GhsB were found to be CckA-dependent RcGTA maturation factors, as GhsA- and GhsB-deficient particles were found to have altered native-gel electrophoresis migration. Additionally, we provide electron microscopy images showing that RcGTA contains side tail fibers and a baseplate-like structure near the tip of the tail, which are independent of ghsB.
authors.affiliation: Department of Microbiology and Immunology, The University of British Columbia, Vancouver, BC, Canada V6T 1Z3.
authors.forename: Alexander B
authors.initials: AB
authors.lastname: Westbye
authors.affiliation: Department of Microbiology and Immunology, The University of British Columbia, Vancouver, BC, Canada V6T 1Z3.
authors.forename: Kevin
authors.initials: K
authors.lastname: Kuchinski
authors.affiliation: Department of Biochemistry and Molecular Biology, The University of British Columbia, Vancouver, BC, Canada V6T 1Z3.
authors.forename: Calvin K
authors.initials: CK
authors.lastname: Yip
authors.affiliation: Department of Microbiology and Immunology, The University of British Columbia, Vancouver, BC, Canada V6T 1Z3. Electronic address: j.beatty@ubc.ca.
authors.forename: J Thomas
authors.initials: JT
authors.lastname: Beatty
mesh_terms: D016667:Bacterial Capsules / Q000378:metabolism*; D001435:Bacteriophages / Q000235:genetics / Q000502:physiology* / Q000648:ultrastructure; D002213:Capsid / Q000378:metabolism* / Q000648:ultrastructure; D005814:Genes, Viral; D046529:Microscopy, Electron, Transmission; D016354:Rhodobacter capsulatus / Q000378:metabolism* / Q000821:virology*; D053585:Virus Attachment
keywords: CBM; CtrA; TEM; phage; receptor