PMID:21439834

Citation	Tang, J, Lander, GC, Olia, AS, Olia, A, Li, R, Casjens, S, Prevelige, P Jr, Cingolani, G, Baker, TS and Johnson, JE (2011) Peering down the barrel of a bacteriophage portal: the genome packaging and release valve in p22. Structure 19:496-502
Abstract	The encapsidated genome in all double-strand DNA bacteriophages is packaged to liquid crystalline density through a unique vertex in the procapsid assembly intermediate, which has a portal protein dodecamer in place of five coat protein subunits. The portal orchestrates DNA packaging and exit, through a series of varying interactions with the scaffolding, terminase, and closure proteins. Here, we report an asymmetric cryoEM reconstruction of the entire P22 virion at 7.8 Å resolution. X-ray crystal structure models of the full-length portal and of the portal lacking 123 residues at the C terminus in complex with gene product 4 (Δ123portal-gp4) obtained by Olia et al. (2011) were fitted into this reconstruction. The interpreted density map revealed that the 150 Å, coiled-coil, barrel portion of the portal entraps the last DNA to be packaged and suggests a mechanism for head-full DNA signaling and transient stabilization of the genome during addition of closure proteins.
Links	PubMed PMC3075339 Online version:10.1016/j.str.2011.02.010
Keywords	Bacteriophage P22/chemistry; Bacteriophage P22/genetics; Bacteriophage P22/ultrastructure; Capsid Proteins/chemistry; Capsid Proteins/genetics; Capsid Proteins/metabolism; Cryoelectron Microscopy; Crystallography, X-Ray; DNA, Viral/chemistry; DNA, Viral/genetics; Genome, Viral/genetics; Models, Molecular; Mutation; Protein Binding; Protein Conformation; Viral Proteins/chemistry; Viral Proteins/metabolism; Virion/chemistry; Virion/genetics; Virion/ultrastructure; Virus Assembly/genetics
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
BPP22:EXLYS		GO:0019073: viral DNA genome packaging	ECO:0000314:		P		Comparing the portal position in the procapsid and the virion shows that the portal increases its contact with the capsid shell during maturation (Figure S1). We propose that this portion of the scaffold remains in place during dsDNA packaging, allowing access of the gp4 C terminus to the bottom of the portal. When gp4 binds, the scaffold protein is displaced allowing the final conformational change implied by the position of the gp4-C-terminal polypeptide that is wedged between the capsid and portal.	complete CACAO 12035

References

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