title: Role of phosphate groups on antiviral activity of casein phosphopeptide against feline calicivirus as a surrogate for norovirus.
abstract: BACKGROUND
  Current research on the gastrointestinal digestion of milk-casein strongly suggests the existence of novel bioactive peptides with antiviral activities that are attributable to their immunostimulatory effects. In the present study, we investigated the antiviral activity of casein peptides rich in phosphate groups, such as casein phosphopeptide (CPP-III).
  
  
  RESULTS
  We prepared two types of CPP with different phosphorylation levels to clarify the role of the phosphate group. Further phosphorylation of CPP-III was conducted by dry heating with sodium pyrophosphate, whereas dephosphorylation was performed enzymatically using alkaline phosphatase and alkaline treatment. Feline calicivirus (FCV) strain F9, a typical norovirus surrogate, and Crandell Rees feline kidney cells were used as the target virus and host cells, respectively. Antiviral activity was determined based on the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and quantitative polymerase chain reaction quantification of antiviral cytokine mRNA expression. Higher cell viability was observed in the host cells treated with phosphorylated CPP-III, and a significant up-regulation of type 1 interferon expression was induced compared to that treated with native CPP-III. However, dephosphorylation of CPP-III resulted in a decrease in the anti-FCV effect.
  
  
  CONCLUSIONS
  The CPP effect was enhanced by the introduction of additional phosphates and conversely weakened by their elimination. Therefore, CPP-III phosphorylation represents an emerging approach for the production of food-grade antiviral agents. © 2016 Society of Chemical Industry.
authors.affiliation: Graduate School of Agriculture, Shinshu University, 8304 Minamiminowa, Ina, Nagano, 399-4598, Japan.
authors.forename: Ntshepisa
authors.initials: N
authors.lastname: Lebetwa
authors.affiliation: Department of Interdisciplinary Genome Sciences and Cell Metabolism, Institute for Biomedical Sciences, Interdisciplinary Cluster for Cutting Edge Research, Shinshu University, Ina, Nagano, 399-4598, Japan.
authors.forename: Takakazu
authors.initials: T
authors.lastname: Mitani
authors.affiliation: Graduate School of Agriculture, Shinshu University, 8304 Minamiminowa, Ina, Nagano, 399-4598, Japan.
authors.forename: Soichiro
authors.initials: S
authors.lastname: Nakamura
authors.affiliation: Graduate School of Agriculture, Shinshu University, 8304 Minamiminowa, Ina, Nagano, 399-4598, Japan.
authors.forename: Shigeru
authors.initials: S
authors.lastname: Katayama
mesh_terms: D000818:Animals; D000998:Antiviral Agents / Q000737:chemistry* / Q000494:pharmacology*; D017250:Caliciviridae Infections / Q000821:virology; D017927:Calicivirus, Feline / Q000187:drug effects* / Q000502:physiology; D002364:Caseins / Q000737:chemistry*; D002415:Cats; D002417:Cattle; D006801:Humans; D008892:Milk / Q000737:chemistry; D029322:Norovirus / Q000187:drug effects* / Q000502:physiology; D010710:Phosphates / Q000737:chemistry; D010748:Phosphopeptides / Q000737:chemistry* / Q000494:pharmacology*; D038301:Virus Inactivation / Q000187:drug effects
chemical_list: D000998:Antiviral Agents; D002364:Caseins; D010710:Phosphates; D010748:Phosphopeptides
keywords: antiviral activity; casein phosphopeptide; norovirus; phosphorylation; type 1 interferon