Localization of the Houdinisome (Ejection Proteins) inside the Bacteriophage P22 Virion by Bubblegram Imaging

ABSTRACT The P22 capsid is a T=7 icosahedrally symmetric protein shell with a portal protein dodecamer at one 5-fold vertex. Extending outwards from that vertex is a short tail, and putatively extending inwards is a 15-nm-long α-helical barrel formed by the C-terminal domains of portal protein subun...

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Autores principales:	Weimin Wu, Justin C. Leavitt, Naiqian Cheng, Eddie B. Gilcrease, Tina Motwani, Carolyn M. Teschke, Sherwood R. Casjens, Alasdair C. Steven
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Lenguaje:	EN
Publicado:	American Society for Microbiology 2016
Materias:	Microbiology QR1-502
Acceso en línea:	https://doaj.org/article/9b9b267307a1486f8926e69d4dbbe79f
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spelling	oai:doaj.org-article:9b9b267307a1486f8926e69d4dbbe79f2021-11-15T15:50:19ZLocalization of the Houdinisome (Ejection Proteins) inside the Bacteriophage P22 Virion by Bubblegram Imaging10.1128/mBio.01152-162150-7511https://doaj.org/article/9b9b267307a1486f8926e69d4dbbe79f2016-09-01T00:00:00Zhttps://journals.asm.org/doi/10.1128/mBio.01152-16https://doaj.org/toc/2150-7511ABSTRACT The P22 capsid is a T=7 icosahedrally symmetric protein shell with a portal protein dodecamer at one 5-fold vertex. Extending outwards from that vertex is a short tail, and putatively extending inwards is a 15-nm-long α-helical barrel formed by the C-terminal domains of portal protein subunits. In addition to the densely packed genome, the capsid contains three “ejection proteins” (E-proteins [gp7, gp16, and gp20]) destined to exit from the tightly sealed capsid during the process of DNA delivery into target cells. We estimated their copy numbers by quantitative SDS-PAGE as approximately 12 molecules per virion of gp16 and gp7 and 30 copies of gp20. To localize them, we used bubblegram imaging, an adaptation of cryo-electron microscopy in which gaseous bubbles induced in proteins by prolonged irradiation are used to map the proteins’ locations. We applied this technique to wild-type P22, a triple mutant lacking all three E-proteins, and three mutants each lacking one E-protein. We conclude that all three E-proteins are loosely clustered around the portal axis, in the region displaced radially inwards from the portal crown. The bubblegram data imply that approximately half of the α-helical barrel seen in the portal crystal structure is disordered in the mature virion, and parts of the disordered region present binding sites for E-proteins. Thus positioned, the E-proteins are strategically placed to pass down the shortened barrel and through the portal ring and the tail, as they exit from the capsid during an infection. IMPORTANCE While it has long been appreciated that capsids serve as delivery vehicles for viral genomes, there is now growing awareness that viruses also deliver proteins into their host cells. P22 has three such proteins (ejection proteins [E-proteins]), whose initial locations in the virion have remained unknown despite their copious amounts (total of 2.5 MDa). This study succeeded in localizing them by the novel technique of bubblegram imaging. The P22 E-proteins are seen to be distributed around the orifice of the portal barrel. Interestingly, this barrel, 15 nm long in a crystal structure, is only about half as long in situ: the remaining, disordered, portion appears to present binding sites for E-proteins. These observations document a spectacular example of a regulatory order-disorder transition in a supramolecular system and demonstrate the potential of bubblegram imaging to map the components of other viruses as well as cellular complexes.Weimin WuJustin C. LeavittNaiqian ChengEddie B. GilcreaseTina MotwaniCarolyn M. TeschkeSherwood R. CasjensAlasdair C. StevenAmerican Society for MicrobiologyarticleMicrobiologyQR1-502ENmBio, Vol 7, Iss 4 (2016)
institution	DOAJ
collection	DOAJ
language	EN
topic	Microbiology QR1-502
spellingShingle	Microbiology QR1-502 Weimin Wu Justin C. Leavitt Naiqian Cheng Eddie B. Gilcrease Tina Motwani Carolyn M. Teschke Sherwood R. Casjens Alasdair C. Steven Localization of the Houdinisome (Ejection Proteins) inside the Bacteriophage P22 Virion by Bubblegram Imaging
description	ABSTRACT The P22 capsid is a T=7 icosahedrally symmetric protein shell with a portal protein dodecamer at one 5-fold vertex. Extending outwards from that vertex is a short tail, and putatively extending inwards is a 15-nm-long α-helical barrel formed by the C-terminal domains of portal protein subunits. In addition to the densely packed genome, the capsid contains three “ejection proteins” (E-proteins [gp7, gp16, and gp20]) destined to exit from the tightly sealed capsid during the process of DNA delivery into target cells. We estimated their copy numbers by quantitative SDS-PAGE as approximately 12 molecules per virion of gp16 and gp7 and 30 copies of gp20. To localize them, we used bubblegram imaging, an adaptation of cryo-electron microscopy in which gaseous bubbles induced in proteins by prolonged irradiation are used to map the proteins’ locations. We applied this technique to wild-type P22, a triple mutant lacking all three E-proteins, and three mutants each lacking one E-protein. We conclude that all three E-proteins are loosely clustered around the portal axis, in the region displaced radially inwards from the portal crown. The bubblegram data imply that approximately half of the α-helical barrel seen in the portal crystal structure is disordered in the mature virion, and parts of the disordered region present binding sites for E-proteins. Thus positioned, the E-proteins are strategically placed to pass down the shortened barrel and through the portal ring and the tail, as they exit from the capsid during an infection. IMPORTANCE While it has long been appreciated that capsids serve as delivery vehicles for viral genomes, there is now growing awareness that viruses also deliver proteins into their host cells. P22 has three such proteins (ejection proteins [E-proteins]), whose initial locations in the virion have remained unknown despite their copious amounts (total of 2.5 MDa). This study succeeded in localizing them by the novel technique of bubblegram imaging. The P22 E-proteins are seen to be distributed around the orifice of the portal barrel. Interestingly, this barrel, 15 nm long in a crystal structure, is only about half as long in situ: the remaining, disordered, portion appears to present binding sites for E-proteins. These observations document a spectacular example of a regulatory order-disorder transition in a supramolecular system and demonstrate the potential of bubblegram imaging to map the components of other viruses as well as cellular complexes.
format	article
author	Weimin Wu Justin C. Leavitt Naiqian Cheng Eddie B. Gilcrease Tina Motwani Carolyn M. Teschke Sherwood R. Casjens Alasdair C. Steven
author_facet	Weimin Wu Justin C. Leavitt Naiqian Cheng Eddie B. Gilcrease Tina Motwani Carolyn M. Teschke Sherwood R. Casjens Alasdair C. Steven
author_sort	Weimin Wu
title	Localization of the Houdinisome (Ejection Proteins) inside the Bacteriophage P22 Virion by Bubblegram Imaging
title_short	Localization of the Houdinisome (Ejection Proteins) inside the Bacteriophage P22 Virion by Bubblegram Imaging
title_full	Localization of the Houdinisome (Ejection Proteins) inside the Bacteriophage P22 Virion by Bubblegram Imaging
title_fullStr	Localization of the Houdinisome (Ejection Proteins) inside the Bacteriophage P22 Virion by Bubblegram Imaging
title_full_unstemmed	Localization of the Houdinisome (Ejection Proteins) inside the Bacteriophage P22 Virion by Bubblegram Imaging
title_sort	localization of the houdinisome (ejection proteins) inside the bacteriophage p22 virion by bubblegram imaging
publisher	American Society for Microbiology
publishDate	2016
url	https://doaj.org/article/9b9b267307a1486f8926e69d4dbbe79f
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Localization of the Houdinisome (Ejection Proteins) inside the Bacteriophage P22 Virion by Bubblegram Imaging

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