title: Quantitative Evaluation of Protein Heterogeneity within Herpes Simplex Virus 1 Particles.
abstract: Several virulence genes have been identified thus far in the herpes simplex virus 1 genome. It is also generally accepted that protein heterogeneity among virions further impacts viral fitness. However, linking this variability directly with infectivity has been challenging at the individual viral particle level. To address this issue, we resorted to flow cytometry (flow virometry), a powerful approach we recently employed to analyze individual viral particles, to identify which tegument proteins vary and directly address if such variability is biologically relevant. We found that the stoichiometry of the UL37, ICP0, and VP11/12 tegument proteins in virions is more stable than the VP16 and VP22 tegument proteins, which varied significantly among viral particles. Most interestingly, viruses sorted for their high VP16 or VP22 content yielded modest but reproducible increases in infectivity compared to their corresponding counterparts containing low VP16 or VP22 content. These findings were corroborated for VP16 in short interfering RNA experiments but proved intriguingly more complex for VP22. An analysis by quantitative Western blotting revealed substantial alterations of virion composition upon manipulation of individual tegument proteins and suggests that VP22 protein levels acted indirectly on viral fitness. These findings reaffirm the interdependence of the virion components and corroborate that viral fitness is influenced not only by the genome of viruses but also by the stoichiometry of proteins within each virion.IMPORTANCEThe ability of viruses to spread in animals has been mapped to several viral genes, but other factors are clearly involved, including virion heterogeneity. To directly probe whether the latter influences viral fitness, we analyzed the protein content of individual herpes simplex virus 1 particles using an innovative flow cytometry approach. The data confirm that some viral proteins are incorporated in more controlled amounts, while others vary substantially. Interestingly, this correlates with the VP16trans-activating viral protein and indirectly with VP22, a second virion component whose modulation profoundly alters virion composition. This reaffirms that not only the presence but also the amount of specific tegument proteins is an important determinant of viral fitness.
authors.affiliation: Department of Pathology and Cell Biology, University of Montreal, Montreal, Quebec, Canada.
authors.forename: Nabil
authors.initials: N
authors.lastname: El Bilali
authors.affiliation: Department of Pathology and Cell Biology, University of Montreal, Montreal, Quebec, Canada.
authors.forename: Johanne
authors.initials: J
authors.lastname: Duron
authors.affiliation: Department of Pathology and Cell Biology, University of Montreal, Montreal, Quebec, Canada.
authors.forename: Diane
authors.initials: D
authors.lastname: Gingras
authors.affiliation: Department of Pathology and Cell Biology, University of Montreal, Montreal, Quebec, Canada roger.lippe@umontreal.ca.
authors.forename: Roger
authors.identifier: http://orcid.org/0000-0001-5066-3070
authors.initials: R
authors.lastname: Lippé
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002522:Chlorocebus aethiops; D005434:Flow Cytometry; D005814:Genes, Viral; D017405:Herpes Simplex Virus Protein Vmw65 / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D018259:Herpesvirus 1, Human / Q000235:genetics* / Q000472:pathogenicity / Q000502:physiology*; D034741:RNA, Small Interfering; D014709:Vero Cells; D015678:Viral Structural Proteins / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D014771:Virion / Q000235:genetics / Q000502:physiology; D019065:Virus Assembly
chemical_list: D017405:Herpes Simplex Virus Protein Vmw65; D034741:RNA, Small Interfering; D015678:Viral Structural Proteins; C073413:herpes simplex virus type 1 protein VP22
keywords: FACS; HSV-1; VP16; VP22; flow cytometry; flow virometry; herpes simplex virus; heterogeneity; tegument; viral particle