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Journal of virology1990; 64(2); 563-573; doi: 10.1128/JVI.64.2.563-573.1990

Three-dimensional structures of maturable and abortive capsids of equine herpesvirus 1 from cryoelectron microscopy.

Abstract: Cryoelectron microscopy and three-dimensional computer reconstruction techniques have been used to compare the structures of two types of DNA-free capsids of equine herpesvirus 1 at a resolution of 4.5 nm. "Light" capsids are abortive, whereas "intermediate" capsids are related to maturable intracellular precursors. Their T = 16 icosahedral outer shells, approximately 125 nm in diameter, are indistinguishable and may be described in terms of three layers of density, totalling 15 nm in thickness. The outermost layer consists of protruding portions of both the hexon and the penton capsomers, rising approximately 5 nm above a midlayer of density. The innermost layer, or "floor," is a 4-nm-thick sheet of virtually continuous density except for the orifices of the channels that traverse each capsomer. Hexon protrusions are distinctly hexagonal in shape, and penton protrusions are pentagonal. The structures of the three kinds of hexons (distinguished according to their positions on the surface lattice) are closely similar but differ somewhat in their respective orientations and in the shapes of their channels. The most prominent features of the midlayer are threefold nodules ("triplexes") at the trigonal lattice points. By analogy with other viral capsids, the triplexes may represent trimers of another capsid protein, possibly VP23 (36 kilodaltons [kDa]) or VP26 (12 kDa). Intermediate capsids differ from light capsids, which are empty, in having one or more internal components. In individual images from which the shell structure has been filtered away, these components are seen to have dimensions of 20 to 30 nm but to lack a visible substructure. This material--which is smeared out in the reconstruction, implying that its distribution is not icosahedrally symmetric or necessarily consistent from particle to particle--consists of aggregates of VP22 (46 kDa). From several lines of evidence, we conclude that this protein is located entirely within the capsid shell. These aggregates may be the remnants of morphogenetic cores retained in capsids interrupted in the process of DNA packaging.
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Publication Date: 1990-02-01 PubMed ID: 2153224PubMed Central: PMC249145DOI: 10.1128/JVI.64.2.563-573.1990Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

This study used cryoelectron microscopy and 3D computer reconstruction techniques to compare two types of DNA-free structures of equine herpesvirus 1 – abortive (light) capsids and maturable (intermediate) capsids. The researchers found that these structures, which have their outer shells composed of hexon and penton capsomers, have deviations in their internal components, with intermediate capsids containing internal components possibly made of VP22 protein aggregates.

Methods used and Structures Analysed

  • The researchers utilized cryoelectron microscopy and three-dimensional computer reconstruction techniques to visualize and compare two types of DNA-free capsids of equine herpesvirus 1.
  • These capsids were classified as “light” and “intermediate” capsids – the former are considered abortive, or failed structures, while the latter are related to maturable intracellular precursors, or pre-stage forms of the virus.
  • Both types of capsids have T = 16 icosahedral outer shells, measured to be about 125 nanometers in diameter.

Outer Shell and Inner Floor Description

  • The outer shell of the capsids consists of three density layers totaling 15 nanometers in thickness.
  • At the very outermost, there are protruding portions of both hexon and penton capsomers.
  • These protrusions are pentagonal for penton capsomers and distinctly hexagonal for hexon capsomers.
  • Beneath these protrusions lies a midlayer of the shell. The most prominent features of this midlayer are threefold nodules, also known as “triplexes,” found at spherical lattice points.
  • The innermost layer, also referred to as the “floor,” is a 4-nanometer-thick sheet of virtually continuous density, interrupted only by the orifices of channels traversing each capsomer.

Differences between Light and Intermediate Capsids

  • While light capsids are empty, intermediate capsids contain one or multiple internal components. These components, distinguishable when the shell structure is filtered away, range between 20 and 30 nanometers but lack visible substructure.
  • This internal material, which appears smeared in the reconstruction, is made up of aggregates of a protein known as VP22 (46 kilodaltons [kDa]).
  • The distribution of this aggregate protein is not consistent or icosahedrally symmetric from particle to particle, implying variability in its arrangement.

Role of Protein Aggregates

  • The evidence suggests that these VP22 protein aggregates may be remnants of morphogenetic cores retained in capsids that were interrupted during the DNA packaging process. This would indicate that the protein is located entirely within the capsid shell.
  • The findings could provide crucial insights into the life cycle of equine herpesvirus 1 and potential avenues for targeted treatment strategies.

Cite This Article

APA
Baker TS, Newcomb WW, Booy FP, Brown JC, Steven AC. (1990). Three-dimensional structures of maturable and abortive capsids of equine herpesvirus 1 from cryoelectron microscopy. J Virol, 64(2), 563-573. https://doi.org/10.1128/JVI.64.2.563-573.1990

Publication

Journal of virology
ISSN: 0022-538X
NlmUniqueID: 0113724
Country: United States
Language: English
Volume: 64
Issue: 2
Pages: 563-573

Researcher Affiliations

Baker, T S
  • Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907.
Newcomb, W W
    Booy, F P
      Brown, J C
        Steven, A C

          MeSH Terms

          • Animals
          • Capsid / genetics
          • Capsid / isolation & purification
          • Capsid / ultrastructure
          • Computer Simulation
          • Freezing
          • Herpesviridae / growth & development
          • Herpesvirus 1, Equid / growth & development
          • Herpesvirus 1, Equid / ultrastructure
          • L Cells
          • Mice
          • Microscopy, Electron
          • Models, Molecular
          • Protein Conformation

          Grant Funding

          • R37 GM033050 / NIGMS NIH HHS
          • GM33050 / NIGMS NIH HHS
          • GM34036 / NIGMS NIH HHS

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          Citations

          This article has been cited 57 times.
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