Sequence conservation within neutralization epitope regions of VP7 and VP4 proteins of human serotype G4 rotavirus isolates
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E A Palombo1, R F Bishop, R G Cotton
1Department of Gastroenterology, Royal Children's Hospital, Parkville, Victoria, Australia.
Abstract:
Serotype G4 rotavirus isolates causing four separate epidemics of severe diarrhoea in young children in Melbourne, Australia (from 1974-1990) were investigated for sequence variation in genes encoding the outer capsid proteins, VP4 and VP7. Complementary DNA of the gene encoding the major outer capsid neutralization antigen, VP7, of eighteen isolates was synthesized and amplified by coupled reverse transcription and polymerase chain reaction. Direct sequencing methods were used to derive the deduced amino acid sequences of the immunodominant A, B, and C neutralization epitope regions of the protein. Limited variation was observed among all isolates. A threonine to asparagine change in region A, at amino acid 96, was associated with altered binding of serotype G4-specific neutralizing monoclonal antibodies. The VP8* region of the outer capsid protein VP4 (containing the proposed serotype-specific neutralization epitopes) was investigated in eight isolates. This region was found to highly conserved both within Melbourne isolates and in relation to the standard strains Wa, P, and VA70. The characteristic periodicity of occurrence of serotype G4 isolates causing severe diarrhoea in Melbourne children is unlikely to be due to changes in neutralization epitopes located on the outer capsid proteins, VP7 or VP4.
Insights
Sequence variation in rotavirus VP4 and VP7 proteins was studied in Melbourne epidemics. Limited changes were found, suggesting other factors cause G4 rotavirus disease periodicity.
Area of Science:
- Virology
- Immunology
- Epidemiology
Background:
- Rotavirus is a leading cause of severe diarrhea in young children globally.
- Serotype G4 rotavirus has caused multiple epidemics in Melbourne, Australia, between 1974 and 1990.
- Understanding genetic variations in rotavirus outer capsid proteins is crucial for vaccine development and disease control.
Purpose of the Study:
- To investigate sequence variation in the VP4 and VP7 genes of serotype G4 rotavirus isolates from Melbourne epidemics.
- To determine if observed amino acid changes in neutralization epitopes correlate with altered antibody binding.
- To assess the role of VP4 and VP7 sequence variation in the periodicity of G4 rotavirus epidemics.
Main Methods:
- Complementary DNA synthesis from eighteen G4 rotavirus isolates.
- Reverse transcription and polymerase chain reaction amplification of VP7 gene.
- Direct sequencing of VP7 neutralization epitopes (regions A, B, C) and VP4 VP8* region.
- Analysis of amino acid sequences and comparison with standard strains.
Main Results:
- Limited sequence variation was observed in the VP7 protein among the Melbourne isolates.
- A specific threonine to asparagine substitution at amino acid 96 in region A of VP7 altered monoclonal antibody binding.
- The VP8* region of VP4 was highly conserved within Melbourne isolates and compared to standard strains.
- No significant sequence variation in VP4 or VP7 was identified that could explain the epidemic periodicity.
Conclusions:
- Sequence variation in the outer capsid proteins VP4 and VP7 is unlikely to be the primary driver for the periodic occurrence of severe G4 rotavirus diarrhea in Melbourne children.
- The identified amino acid change in VP7 warrants further investigation regarding its impact on viral fitness and transmission.
- Further research should explore other potential factors contributing to the epidemic patterns of G4 rotavirus.