Three-dimensional structure of a viral genome-delivery portal vertex

Olia, A. S. et al. Nature Structural and Molecular Biology. 18, 597–604 (2011)

Speaker: Chun-Hsien Fei (費俊憲)                       Time: 14:10~15:00, Sep. 21, 2011

Commentator: Dr. Yu-Chih Lo (羅玉枝 老師)    Place: Room 601

Abstract

Double-stranded DNA viruses such as bacteriophages and herpesviruses deliver their genomic materials through a DNA channel, known as portal proteins. During virus assembly, terminase binds to portal proteins to package DNA into capsid¹. Conversely, portal protein mediates ejection of the genome into the host cell². In this study, the authors reported two three-dimensional structures of dodecameric portal protein of bacteriophage P22. The structure of N-terminal chymotryptic fragment of portal protein (residue 1-602, referred as portal core) was solved to 3.25 Å resolution. The structure shows that portal protein core bound to 12 subunits of gene product 4 (gp4) forming a ~1.1 MDa assembly. The portal-portal monomer interface is stabilized by salt bridges. Each gp4 sits at the interface of two portal protein subunits and the complex is stabilized by salt bridges and hydrogen bonds. The structure of full-length portal protein unveils that C-terminal domain forms a unique ~200-Å-long α-helical barrel. This barrel domain sits deeply into the virion and is highly conserved in the Podoviridae family. The full-length portal protein is composed by a hollow funnel shaped core with an extended rifle barrel, forming a DNA-translocation channel ~40 Å in diameter. This is large enough to accommodate double-stranded linear DNA. The authors proposed that the barrel domain is involved in genome packaging into the capsid and increasing the accuracy of genome ejection into the host cell³. The structural informations  in this paper provides basic knowledge for further studies on the mechanism of genome packaging and ejection.

References

1.     Lander, G. C. et al. Science. 312, 1791-1795 (2006). The Structure of an Infectious P22 Virion Shows the Signal for Headful DNA Packaging

2.     Hartwieg, E et al. Biophysical Journal. 49, 24–26 (1986). DNA injection apparatus of phage P22.

3.     Casjens, S. R. Nature reviews. 9, 647-657 (2011). The DNA-packaging nanomotor of tailed bacteriophages.