DNA binding and condensation properties of the herpes simplex virus type 1 triplex protein VP19C.

Alakesh Bera,Heng Zhu,Jian Zhu,Prashant Desai,Edward M Perkins,Robert J Geraghty

doi:10.1371/journal.pone.0104640

Alakesh Bera, Heng Zhu + Show 4 more

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https://doi.org/10.1371/journal.pone.0104640

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Abstract

Herpesvirus capsids are regular icosahedrons with a diameter of a 125 nm and are made up of 162 capsomeres arranged on a T = 16 lattice. The capsomeres (VP5) interact with the triplex structure, which is a unique structural feature of herpesvirus capsid shells. The triplex is a heterotrimeric complex; one molecule of VP19C and two of VP23 form a three-pronged structure that acts to stabilize the capsid shell through interactions with adjacent capsomeres. VP19C interacts with VP23 and with the major capsid protein VP5 and is required for the nuclear localization of VP23. Mutation of VP19C results in the abrogation of capsid shell synthesis. Analysis of the sequence of VP19C showed the N-terminus of VP19C is very basic and glycine rich. It was hypothesized that this domain could potentially bind to DNA. In this study an electrophoretic mobility shift assay (EMSA) and a DNA condensation assay were performed to demonstrate that VP19C can bind DNA. Purified VP19C was able to bind to both a DNA fragment of HSV-1 origin as well as a bacterial plasmid sequence indicating that this activity is non-specific. Ultra-structural imaging of the nucleo-protein complexes revealed that VP19C condensed the DNA and forms toroidal DNA structures. Both the DNA binding and condensing properties of VP19C were mapped to the N-terminal 72 amino acids of the protein. Mutational studies revealed that the positively charged arginine residues in this N-terminal domain are required for this binding. This DNA binding activity, which resides in a non-conserved region of the protein could be required for stabilization of HSV-1 DNA association in the capsid shell.

Highlights

The herpesvirus particle consists of four distinct structural layers
In that study capsid proteins were transferred to a nitrocellulose membrane and a radiolabeled probe corresponding to the junction fragment of HSV-1 bound to a polypeptide with the same mobility as VP19C
Radioactivity corresponding to a retarded DNA-protein complex was detected when VP19C was mixed with the probe

Summary

Introduction

The herpesvirus particle consists of four distinct structural layers. The outermost layer is an envelope in which are embedded the virus glycoproteins; the envelop encloses the tegument layer which is attached to the capsid, the viral protein coat; and the capsid encases and protects the virus genome [1,2]. The capsid is an icosahedron made of four shell proteins that lie on a T = 16 icosahedral lattice [3]. These proteins are the major capsid protein, VP5, the triplex proteins, VP19C and VP23 and the small capsid protein, VP26 [4,5]. The shell contains four structural elements the hexon, the penton, the triplex and the portal. The triplex, which is a characteristic structural feature of all herpesvirus capsids, is a hetero-trimer of VP19C (50 kDa) and two molecules of VP23 (34 kDa). The triplex acts to stabilize and facilitate capsid shell synthesis by interaction with adjacent hexons or pentons. VP5, VP19C and VP23 are all essential for capsid assembly in HSV-1 infected cells [6,7,8]

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