PMID:24126213

Citation	Padilla-Sanchez, V, Gao, S, Kim, HR, Kihara, D, Sun, L, Rossmann, MG and Rao, VB (2014) Structure-function analysis of the DNA translocating portal of the bacteriophage T4 packaging machine. J. Mol. Biol. 426:1019-38
Abstract	Tailed bacteriophages and herpesviruses consist of a structurally well conserved dodecameric portal at a special 5-fold vertex of the capsid. The portal plays critical roles in head assembly, genome packaging, neck/tail attachment, and genome ejection. Although the structures of portals from phages φ29, SPP1, and P22 have been determined, their mechanistic roles have not been well understood. Structural analysis of phage T4 portal (gp20) has been hampered because of its unusual interaction with the Escherichia coli inner membrane. Here, we predict atomic models for the T4 portal monomer and dodecamer, and we fit the dodecamer into the cryo-electron microscopy density of the phage portal vertex. The core structure, like that from other phages, is cone shaped with the wider end containing the "wing" and "crown" domains inside the phage head. A long "stem" encloses a central channel, and a narrow "stalk" protrudes outside the capsid. A biochemical approach was developed to analyze portal function by incorporating plasmid-expressed portal protein into phage heads and determining the effect of mutations on head assembly, DNA translocation, and virion production. We found that the protruding loops of the stalk domain are involved in assembling the DNA packaging motor. A loop that connects the stalk to the channel might be required for communication between the motor and the portal. The "tunnel" loops that project into the channel are essential for sealing the packaged head. These studies established that the portal is required throughout the DNA packaging process, with different domains participating at different stages of genome packaging.
Links	PubMed PMC3944221 Online version:10.1016/j.jmb.2013.10.011
Keywords	Bacteriophage T4/chemistry; Bacteriophage T4/genetics; Bacteriophage T4/metabolism; Capsid Proteins/chemistry; Capsid Proteins/genetics; Capsid Proteins/metabolism; DNA Packaging/physiology; DNA, Viral/chemistry; DNA, Viral/genetics; Escherichia coli/virology; Models, Molecular; Protein Conformation; Protein Folding; Virion/genetics; Virus Assembly/physiology
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
BPT4:PORTL		GO:0046718: viral entry into host cell	ECO:0000314:		P		This protein aids in head assembly, genome packaging, and genome injection. The most common function is of a portal protein that aids in infection by forming a channel, connecting the phage to the membrane of the host bacteria. See Figure 5 for complete outline and analysis of function.	complete CACAO 11979

References

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