Related Experiment Video
Updated: Jun 14, 2026

Following Cell-fate in E. coli After Infection by Phage Lambda
Published on: October 14, 2011
Structure of lactococcal phage p2 baseplate and its mechanism of activation
Giuliano Sciara1, Cecilia Bebeacua, Patrick Bron
1Architecture 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.
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.
Related Concept Videos
Lytic Cycle of Bacteriophages
DNA Bacteriophages
Viral Replication: Lytic Cycle
Lysogenic Cycle of Bacteriophages
Viral Replication: Lysogenic Cycle
Viral Structure

