Structure of lactococcal phage p2 baseplate and its mechanism of activation.
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.
Sciara
Giuliano
G
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.
Bebeacua
Cecilia
C
Bron
Patrick
P
Tremblay
Denise
D
Ortiz-Lombardia
Miguel
M
Lichière
Julie
J
van Heel
Marin
M
Campanacci
Valérie
V
Moineau
Sylvain
S
Cambillau
Christian
C
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*
D002412:Cations; D017376:Viral Tail Proteins; D002118:Calcium