Subassemblies and Asymmetry in Assembly of Herpes Simplex Virus Procapsid

ABSTRACT The herpes simplex virus 1 (HSV-1) capsid is a massive particle (~200 MDa; 1,250-Å diameter) with T=16 icosahedral symmetry. It initially assembles as a procapsid with ~4,000 protein subunits of 11 different kinds. The procapsid undergoes major changes in structure and composition as it mat...

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Autores principales:	Anastasia A. Aksyuk, William W. Newcomb, Naiqian Cheng, Dennis C. Winkler, Juan Fontana, J. Bernard Heymann, Alasdair C. Steven
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Lenguaje:	EN
Publicado:	American Society for Microbiology 2015
Materias:	Microbiology QR1-502
Acceso en línea:	https://doaj.org/article/ee0b7911acdd41b680069a561c4ef247
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spelling	oai:doaj.org-article:ee0b7911acdd41b680069a561c4ef2472021-11-15T15:41:31ZSubassemblies and Asymmetry in Assembly of Herpes Simplex Virus Procapsid10.1128/mBio.01525-152150-7511https://doaj.org/article/ee0b7911acdd41b680069a561c4ef2472015-10-01T00:00:00Zhttps://journals.asm.org/doi/10.1128/mBio.01525-15https://doaj.org/toc/2150-7511ABSTRACT The herpes simplex virus 1 (HSV-1) capsid is a massive particle (~200 MDa; 1,250-Å diameter) with T=16 icosahedral symmetry. It initially assembles as a procapsid with ~4,000 protein subunits of 11 different kinds. The procapsid undergoes major changes in structure and composition as it matures, a process driven by proteolysis and expulsion of the internal scaffolding protein. Assembly also relies on an external scaffolding protein, the triplex, an α2β heterotrimer that coordinates neighboring capsomers in the procapsid and becomes a stabilizing clamp in the mature capsid. To investigate the mechanisms that regulate its assembly, we developed a novel isolation procedure for the metastable procapsid and collected a large set of cryo-electron microscopy data. In addition to procapsids, these preparations contain maturation intermediates, which were distinguished by classifying the images and calculating a three-dimensional reconstruction for each class. Appraisal of the procapsid structure led to a new model for assembly; in it, the protomer (assembly unit) consists of one triplex, surrounded by three major capsid protein (MCP) subunits. The model exploits the triplexes’ departure from 3-fold symmetry to explain the highly skewed MCP hexamers, the triplex orientations at each 3-fold site, and the T=16 architecture. These observations also yielded new insights into maturation. IMPORTANCE This paper addresses the molecular mechanisms that govern the self-assembly of large, structurally complex, macromolecular particles, such as the capsids of double-stranded DNA viruses. Although they may consist of thousands of protein subunits of many different kinds, their assembly is precise, ranking them among the largest entities in the biosphere whose structures are uniquely defined to the atomic level. Assembly proceeds in two stages: formation of a precursor particle (procapsid) and maturation, during which major changes in structure and composition take place. Our analysis of the HSV procapsid by cryo-electron microscopy suggests a hierarchical pathway in which multisubunit “protomers” are the building blocks of the procapsid but their subunits are redistributed into different subcomplexes upon being incorporated into a nascent procapsid and are redistributed again in maturation. Assembly is a highly virus-specific process, making it a potential target for antiviral intervention.Anastasia A. AksyukWilliam W. NewcombNaiqian ChengDennis C. WinklerJuan FontanaJ. Bernard HeymannAlasdair C. StevenAmerican Society for MicrobiologyarticleMicrobiologyQR1-502ENmBio, Vol 6, Iss 5 (2015)
institution	DOAJ
collection	DOAJ
language	EN
topic	Microbiology QR1-502
spellingShingle	Microbiology QR1-502 Anastasia A. Aksyuk William W. Newcomb Naiqian Cheng Dennis C. Winkler Juan Fontana J. Bernard Heymann Alasdair C. Steven Subassemblies and Asymmetry in Assembly of Herpes Simplex Virus Procapsid
description	ABSTRACT The herpes simplex virus 1 (HSV-1) capsid is a massive particle (~200 MDa; 1,250-Å diameter) with T=16 icosahedral symmetry. It initially assembles as a procapsid with ~4,000 protein subunits of 11 different kinds. The procapsid undergoes major changes in structure and composition as it matures, a process driven by proteolysis and expulsion of the internal scaffolding protein. Assembly also relies on an external scaffolding protein, the triplex, an α2β heterotrimer that coordinates neighboring capsomers in the procapsid and becomes a stabilizing clamp in the mature capsid. To investigate the mechanisms that regulate its assembly, we developed a novel isolation procedure for the metastable procapsid and collected a large set of cryo-electron microscopy data. In addition to procapsids, these preparations contain maturation intermediates, which were distinguished by classifying the images and calculating a three-dimensional reconstruction for each class. Appraisal of the procapsid structure led to a new model for assembly; in it, the protomer (assembly unit) consists of one triplex, surrounded by three major capsid protein (MCP) subunits. The model exploits the triplexes’ departure from 3-fold symmetry to explain the highly skewed MCP hexamers, the triplex orientations at each 3-fold site, and the T=16 architecture. These observations also yielded new insights into maturation. IMPORTANCE This paper addresses the molecular mechanisms that govern the self-assembly of large, structurally complex, macromolecular particles, such as the capsids of double-stranded DNA viruses. Although they may consist of thousands of protein subunits of many different kinds, their assembly is precise, ranking them among the largest entities in the biosphere whose structures are uniquely defined to the atomic level. Assembly proceeds in two stages: formation of a precursor particle (procapsid) and maturation, during which major changes in structure and composition take place. Our analysis of the HSV procapsid by cryo-electron microscopy suggests a hierarchical pathway in which multisubunit “protomers” are the building blocks of the procapsid but their subunits are redistributed into different subcomplexes upon being incorporated into a nascent procapsid and are redistributed again in maturation. Assembly is a highly virus-specific process, making it a potential target for antiviral intervention.
format	article
author	Anastasia A. Aksyuk William W. Newcomb Naiqian Cheng Dennis C. Winkler Juan Fontana J. Bernard Heymann Alasdair C. Steven
author_facet	Anastasia A. Aksyuk William W. Newcomb Naiqian Cheng Dennis C. Winkler Juan Fontana J. Bernard Heymann Alasdair C. Steven
author_sort	Anastasia A. Aksyuk
title	Subassemblies and Asymmetry in Assembly of Herpes Simplex Virus Procapsid
title_short	Subassemblies and Asymmetry in Assembly of Herpes Simplex Virus Procapsid
title_full	Subassemblies and Asymmetry in Assembly of Herpes Simplex Virus Procapsid
title_fullStr	Subassemblies and Asymmetry in Assembly of Herpes Simplex Virus Procapsid
title_full_unstemmed	Subassemblies and Asymmetry in Assembly of Herpes Simplex Virus Procapsid
title_sort	subassemblies and asymmetry in assembly of herpes simplex virus procapsid
publisher	American Society for Microbiology
publishDate	2015
url	https://doaj.org/article/ee0b7911acdd41b680069a561c4ef247
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Subassemblies and Asymmetry in Assembly of Herpes Simplex Virus Procapsid

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