Summary auto-generated
This study examined herpesvirus capsid assembly by comparing the scaffolding proteins of varicella-zoster virus (VZV) and herpes simplex virus type 1 (HSV-1). Researchers expressed VZV genes 33 and 33-5, encoding a protease and major scaffolding protein, in insect cells using baculovirus vectors. The VZV scaffolding protein formed long, flexible, hollow rods, contrasting with HSV-1's protein which forms aggregates. Unlike HSV-1, removing 27 carboxy-terminal amino acids from the VZV scaffolding protein via protease cleavage did not alter its morphology. When cells were co-infected with viruses expressing HSV-1 capsid shell proteins and VZV scaffolding protein, complete capsids assembled, indicating cross-species compatibility. Capsid assembly efficiency increased substantially when the VZV protein's carboxy-terminal 23 amino acids were replaced with HSV-1's corresponding 22 amino acids, demonstrating that this region is critical for proper capsid formation across herpesvirus species.
Key findings
- VZV scaffolding protein forms long, flexible hollow rods in infected cells, structurally distinct from HSV-1 protein aggregates
- Protease cleavage of VZV scaffolding protein does not alter its morphology, unlike HSV-1 where cleavage promotes particle formation
- VZV scaffolding protein can functionally substitute for HSV-1 protein in capsid assembly, indicating cross-species compatibility
- Carboxy-terminal sequences are critical for efficient capsid assembly; swapping VZV's terminal 23 amino acids for HSV-1's terminal 22 amino acids substantially improves capsid formation efficiency
This summary was generated automatically from the article PDF and is not part of the original publication. Refer to the PDF for the authoritative text.
Abstract
The scaffolding protein and associated protease of the human herpesvirus varicella-zoster virus (VZV), encoded by genes 33.5 and 33 respectively, were synthesized in insect cells using a baculovirus expression system. The expressed 33.5 product formed numerous long, flexible, hollow rods, and in this respect different from the herpes simplex virus type 1 (HSV-1) homologue which forms large aggregates consisting mainly of fibrous material interspersed with scaffold-like particles. Removal of 27 amino acids from the carboxy terminus of the VZV scaffolding protein by the gene 33 protease or expression of the cleaved product did not result in any discernible change in the morphology of the scaffolding protein. Again, this was in marked contrast to the situation in HSV-1 where removal of the 25 carboxy- terminal amino acids from the scaffolding protein by the associated protease or expression of VP22a results in the formation of large numbers of scaffold-like particles. Despite these differences, when cells were multiply infected with baculoviruses expressing the HSV-1 capsid shell proteins and the VZV scaffolding protein complete capsids were observed, suggesting that the VZV protein could act as a scaffold for the assembly of the HSV-1 capsid shell. The efficiency of capsid assembly was increased substantially by exchanging the 23 carboxy- terminal amino acids of the VZV scaffolding protein for the corresponding 22 carboxy-terminal amino acids of the HSV-1 homologue, supporting previous work which showed that this region was critical for the formation of intact capsids.