title: Structure of lactococcal phage p2 baseplate and its mechanism of activation.
abstract: Siphoviridae is the most abundant viral family on earth which infects bacteria as well as archaea. All known siphophages infecting gram+ Lactococcus lactis possess a baseplate at the tip of their tail involved in host recognition and attachment. Here, we report analysis of the p2 phage baseplate structure by X-ray crystallography and electron microscopy and propose a mechanism for the baseplate activation during attachment to the host cell. This approximately 1 MDa, Escherichia coli-expressed baseplate is composed of three protein species, including six trimers of the receptor-binding protein (RBP). RBPs host-recognition domains point upwards, towards the capsid, in agreement with the electron-microscopy map of the free virion. In the presence of Ca(2+), a cation mandatory for infection, the RBPs rotated 200 degrees downwards, presenting their binding sites to the host, and a channel opens at the bottom of the baseplate for DNA passage. These conformational changes reveal a novel siphophage activation and host-recognition mechanism leading ultimately to DNA ejection.
authors.affiliation: Architecture et Fonction des Macromolécules Biologiques, UMR 6098 Centre National de la Recherche Scientifique and Universités d'Aix-Marseille I & II, Campus de Luminy, Case 932, 13288 Marseille Cedex 09, France.
authors.forename: Giuliano
authors.initials: G
authors.lastname: Sciara
authors.forename: Cecilia
authors.initials: C
authors.lastname: Bebeacua
authors.forename: Patrick
authors.initials: P
authors.lastname: Bron
authors.forename: Denise
authors.initials: D
authors.lastname: Tremblay
authors.forename: Miguel
authors.initials: M
authors.lastname: Ortiz-Lombardia
authors.forename: Julie
authors.initials: J
authors.lastname: Lichière
authors.forename: Marin
authors.initials: M
authors.lastname: van Heel
authors.forename: Valérie
authors.initials: V
authors.lastname: Campanacci
authors.forename: Sylvain
authors.initials: S
authors.lastname: Moineau
authors.forename: Christian
authors.initials: C
authors.lastname: Cambillau
mesh_terms: D017901:Bacteriophage P2 / Q000378:metabolism*; D001665:Binding Sites; D002118:Calcium / Q000737:chemistry; D002412:Cations; D020285:Cryoelectron Microscopy / Q000379:methods; D018360:Crystallography, X-Ray / Q000379:methods; D004926:Escherichia coli / Q000378:metabolism; D013294:Lactococcus lactis / Q000821:virology; D008854:Microscopy, Electron / Q000379:methods; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D011485:Protein Binding; D011487:Protein Conformation; D017376:Viral Tail Proteins / Q000737:chemistry*
chemical_list: D002412:Cations; D017376:Viral Tail Proteins; D002118:Calcium