The structure of the folded domain from the signature multifunctional protein ICP27 from herpes simplex virus-1 reveals an intertwined dimer

Richard B Tunnicliffe,Alexander P Golovanov,Rozanne M Sandri-Goldin,Thomas A Jowitt,Mitchell Schacht,Colin Levy

doi:10.1038/srep11234

Richard B Tunnicliffe, Alexander P Golovanov + Show 4 more

Open Access

https://doi.org/10.1038/srep11234

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Abstract

Herpesviruses cause life-long infections by evading the host immune system and establishing latent infections. All mammalian herpesviruses express an essential multifunctional protein that is typified by ICP27 encoded by Herpes Simplex Virus 1. The only region that is conserved among the diverse members of the ICP27 family is a predicted globular domain that has been termed the ICP27 homology domain. Here we present the first crystal structure of the ICP27 homology domain, solved to 1.9 Å resolution. The protein is a homo-dimer, adopting a novel intertwined fold with one CHCC zinc-binding site per monomer. The dimerization, which was independently confirmed by SEC-MALS and AUC, is stabilized by an extensive network of intermolecular contacts, and a domain-swap involving the two N-terminal helices and C-terminal tails. Each monomer contains a lid motif that can clamp the C-terminal tail of its dimeric binding partner against its globular core, without forming any distinct secondary structure elements. The binding interface was probed with point mutations, none of which had a noticeable effect on dimer formation; however deletion of the C-terminal tail region prevented dimer formation in vivo. The structure provides a template for future biochemical studies and modelling of ICP27 homologs from other herpesviruses.

Highlights

Binding to cellular proteins to promote the export of intronless viral mRNA via the TAP/NXF1 pathway[11,12]
ICP27 interacts with the mRNA export adaptor protein ALYREF7,11 and it directly interacts with the mRNA exporter receptor TAP/NXF118,19
While some of these interactions have been mapped to the N-terminal half of the protein, such as the interaction with ALYREF, SRPK1 and RNA, a number of interactions have been mapped to the C-terminal globular region, including interactions with SR splicing proteins, translation factors, RNA polymerase II and TAP/NXF1, this domain is of crucial functional importance

Summary

Introduction

Binding to cellular proteins to promote the export of intronless viral mRNA via the TAP/NXF1 pathway[11,12]. ICP27 is predominantly nuclear at early times after infection and it has been found to be associated with splicing complex proteins in its role as an inhibitor of host cell splicing[13] It interacts with the C-terminal domain of cellular RNA polymerase II at early times and is involved in the recruitment of RNA polymerase II to HSV-1 replication sites[16]. A number of ICP27 deletion mutants have been used to map the regions of interaction between ICP27 and its interacting partners While some of these interactions have been mapped to the N-terminal half of the protein, such as the interaction with ALYREF, SRPK1 and RNA, a number of interactions have been mapped to the C-terminal globular region, including interactions with SR splicing proteins, translation factors, RNA polymerase II and TAP/NXF1, this domain is of crucial functional importance. The data establishes the archetype for the novel IHD fold and should inform future functional studies of homologous herpesvirus proteins by allowing more targeted mutations

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