Genetic mechanisms of antigenic variation in infectious bursal disease virus: analysis of a naturally occurring variant virus.
The major immunogenic protein VP2 from a pathogenic field isolate (variant A virus) of infectious bursal disease virus (IBDV) was cloned and sequenced to examine antigenic variations. The VP2 open reading frame consists of 1509 nucleotides and codes for a 503 amino acid protein. Overall, the VP2 amino acid sequence of the variant A virus shares 98.6% identity with VP2 genes from other published IBDV strains. However, within the central region of VP2 (amino acids 222-334) lies a highly divergent area that we have termed the variable domain. Relative to five other IBDV isolates, a total of six amino acid changes occur within the variable domain of the variant A virus. At positions 284-288, a substitution of isoleucine to threonine, a decrease in the number of Chou and Fasman beta turns, and a switch from a hydrophilic to a hydrophobic region are found only in the variant A virus. Together these changes predict a decrease in antigenicity as determined by calculation of potential antigenic sites. This suggests that only minor changes within VP2 contributed to the emergence of a variant virus that can cause disease in immunized birds.
Lana
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DP
U.S. Department of Agriculture, Avian Disease and Oncology Laboratory, East Lansing, Michigan 48823.
Beisel
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CE
Silva
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RF
D000595:Amino Acid Sequence; D000818:Animals; D000940:Antigenic Variation / Q000235:genetics*; D001483:Base Sequence; D002213:Capsid / Q000737:chemistry* / Q000235:genetics / Q000276:immunology; D036022:Capsid Proteins; D002645:Chickens; D003001:Cloning, Molecular; D004279:DNA, Viral / Q000235:genetics; D014644:Genetic Variation / Q000235:genetics*; D007243:Infectious bursal disease virus / Q000235:genetics* / Q000276:immunology; D008969:Molecular Sequence Data
D036022:Capsid Proteins; D004279:DNA, Viral