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Modest truncation of the major capsid protein abrogates B19 parvovirus capsid formation
M Kawase1, M Momoeda, N S Young
1Hematology Branch, National Heart, Lung, and Blood Institute, Bethesda, Maryland 20892, USA.
Abstract:
In vitro studies have suggested an important role for the minor capsid protein (VP1) unique region and the junction between VP1 and the major capsid protein (VP2) in the neutralizing immune response to B19 parvovirus. We investigated the role of the NH2-terminal region of the major structural protein in capsid structure by expressing progressively more truncated versions of the VP2 gene followed by analysis using immunoblotting and electron microscopy of density gradient-purified particles. Deletion of the first 25 amino acids (aa) of VP2 did not affect capsid assembly. Altered VP2 with truncations to aa 26 to 30, including a single amino acid deletion at position 25, failed to self-assemble but did participate with normal VP2 in the capsid structure. The altered region corresponds to the beginning of the beta A antiparallel strand. Truncations beyond aa 30 were incompatible with either self-assembly or coassembly, probably because of deletion of the beta B strand, which helps to form the core structure of the virus.
Insights
The major capsid protein (VP2) NH2-terminal region is crucial for B19 parvovirus assembly. Truncations beyond amino acid 30 disrupt capsid formation, impacting viral structure and immune response.
Area of Science:
- Virology
- Structural Biology
- Immunology
Background:
- The B19 parvovirus capsid structure is essential for its infectivity and immune response.
- Specific regions of capsid proteins, including the minor capsid protein (VP1) unique region and the VP1-VP2 junction, are implicated in immune evasion.
- The role of the NH2-terminal region of the major capsid protein (VP2) in B19 parvovirus capsid assembly remains incompletely understood.
Purpose of the Study:
- To elucidate the role of the NH2-terminal region of the B19 parvovirus VP2 protein in capsid structure and assembly.
- To determine the critical amino acid residues and structural elements within the VP2 NH2-terminus required for proper viral particle formation.
Main Methods:
- Expression and analysis of progressively truncated VP2 gene variants.
- Immunoblotting to detect and characterize VP2 protein fragments.
- Electron microscopy to visualize capsid assembly and structure.
- Density gradient centrifugation for purification of viral particles.
Main Results:
- Deletion of the first 25 amino acids (aa) of VP2 did not impede capsid self-assembly.
- Truncations affecting amino acids 26-30, including a single amino acid deletion at position 25, abolished VP2 self-assembly but allowed incorporation into existing capsids.
- Further truncations beyond aa 30 prevented both self-assembly and co-assembly, indicating the loss of essential structural domains.
- The critical region for assembly involves the beta A and beta B antiparallel strands.
Conclusions:
- The NH2-terminal region of B19 parvovirus VP2, specifically beyond amino acid 30, is indispensable for proper capsid assembly.
- The beta B strand appears to be a key structural component for viral core formation and assembly.
- Understanding these structural requirements can inform strategies targeting B19 parvovirus infectivity and immune interactions.