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Structural proteins of equine arteritis virus
A A de Vries1, E D Chirnside, M C Horzinek
1Department of Infectious Diseases and Immunology, Veterinary Faculty, University of Utrecht, The Netherlands.
Abstract:
We have recently shown that the genome of equine arteritis virus (EAV) contains seven open reading frames (ORFs). We now present data on the structural proteins of EAV and the assignment of their respective genes. Virions are composed of a 14-kDa nucleocapsid protein (N) and three membrane proteins designated M, GS, and GL. M is an unglycosylated protein of 16 kDa, and GS and GL are N-glycosylated proteins of 25 and 30 to 42 kDa, respectively. The broad size distribution of GL results from heterogeneous N-acetyllactosamine addition since it is susceptible to digestion by endo-beta-galactosidase. Using monospecific antisera as well as an antivirion serum, and by expression of individual ORFs, the genes for the structural proteins were identified: ORF 7 codes for N, ORF 6 for M, ORF 5 for GL, and ORF 2 for GS. With the exception of GS, the proteins are about equally abundant in EAV virions, being present at a molar ratio of 3 (N):2 (M):3 (GL). The GS protein, which is expressed at a level similar to that of M in infected cells, is strikingly underrepresented in virus particles (1 to 2%). Our data justify a distinct taxonomic position for EAV, together with lactate dehydrogenase-elevating virus and simian hemorrhagic fever virus; although coronavirus- and toroviruslike in features of transcription and translation, the virion architecture of EAV is fundamentally different.
Insights
Equine arteritis virus (EAV) structural proteins, including nucleocapsid (N) and membrane proteins (M, GS, GL), were identified and their genes assigned. The study reveals distinct virion architecture, supporting EAV
Area of Science:
- Virology
- Molecular Biology
- Protein Chemistry
Background:
- Equine arteritis virus (EAV) genome organization was previously established, revealing seven open reading frames (ORFs).
- Understanding the structural proteins and their genetic origins is crucial for classifying EAV and related viruses.
Purpose of the Study:
- To identify and characterize the structural proteins of Equine arteritis virus (EAV).
- To assign the genes responsible for the synthesis of these structural proteins.
- To determine the relative abundance and post-translational modifications of EAV structural proteins.
Main Methods:
- Analysis of virion composition, including molecular weight determination of nucleocapsid (N) and membrane proteins (M, GS, GL).
- Use of monospecific antisera and antivirion serum for protein identification.
- Expression of individual ORFs to confirm gene assignments for structural proteins.
Main Results:
- EAV virions comprise a 14-kDa nucleocapsid protein (N) and three membrane proteins: M (16 kDa, unglycosylated), GS (25 kDa, N-glycosylated), and GL (30-42 kDa, N-glycosylated).
- Genes encoding structural proteins were assigned: ORF 7 (N), ORF 6 (M), ORF 5 (GL), and ORF 2 (GS).
- Proteins N, M, and GL are abundant in virions (molar ratio ~3:2:3), while GS is significantly underrepresented (1-2%). GL exhibits size heterogeneity due to N-acetyllactosamine addition.
Conclusions:
- The identified structural proteins and their gene assignments provide a comprehensive understanding of EAV virion composition.
- The distinct virion architecture of EAV, despite some transcriptional similarities to coronaviruses and toroviruses, supports its unique taxonomic position.
- Findings contribute to the classification of EAV, lactate dehydrogenase-elevating virus, and simian hemorrhagic fever virus.