Structural Investigation of Orf Virus Bcl-2 Homolog ORFV125 Interactions with BH3-Motifs from BH3-Only Proteins Puma and Hrk.

Chathura D Suraweera,Marc Kvansakul,Mark G Hinds

doi:10.3390/v13071374

Chathura D Suraweera, Marc Kvansakul + Show 1 more

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https://doi.org/10.3390/v13071374

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Journal: Viruses	Publication Date: Jul 15, 2021
Citations: 5	License type: CC BY 4.0

Affiliation: La Trobe University, University of Melbourne

Abstract

Numerous viruses have evolved sophisticated countermeasures to hijack the early programmed cell death of host cells in response to infection, including the use of proteins homologous in sequence or structure to Bcl-2. Orf virus, a member of the parapoxviridae, encodes for the Bcl-2 homolog ORFV125, a potent inhibitor of Bcl-2-mediated apoptosis in the host. ORFV125 acts by directly engaging host proapoptotic Bcl-2 proteins including Bak and Bax as well as the BH3-only proteins Hrk and Puma. Here, we determined the crystal structures of ORFV125 bound to the BH3 motif of proapoptotic proteins Puma and Hrk. The structures reveal that ORFV125 engages proapoptotic BH3 motif peptides using the canonical ligand binding groove. An Arg located in the structurally equivalent BH1 region of ORFV125 forms an ionic interaction with the conserved Asp in the BH3 motif in a manner that mimics the canonical ionic interaction seen in host Bcl-2:BH3 motif complexes. These findings provide a structural basis for Orf virus-mediated inhibition of host cell apoptosis and reveal the flexibility of virus encoded Bcl-2 proteins to mimic key interactions from endogenous host signalling pathways.

Highlights

Viruses utilize numerous immunomodulatory strategies to neutralize host cell apoptosis [1,2,3] to keep them viable for viral replication
We have previously shown that ORF virus-encoded B-cell lymphoma-2 (Bcl-2) homolog ORFV125 has a restricted binding profile towards peptides spanning the BH3 motif (26-mer) of proapoptotic Bcl-2 proteins and binds only human Bak, Bax, Puma and Hrk BH3 motif peptides with nanomolar to sub micromolar affinities [25]
ORFV125 adopts the conserved Bcl-2 fold with seven α-helices in a domain-swapped dimeric configuration (Figure 2A) where the α1 helix of one protomer is swapped with the neighbouring protomer to form the dimer interface as previously seen in other poxvirus genera such as Vaccinia virus (VACV) F1L [27,28] (Figure 2C), variola virus (VARV) F1L [26], DPV022 [29]

Summary

Introduction

Viruses utilize numerous immunomodulatory strategies to neutralize host cell apoptosis [1,2,3] to keep them viable for viral replication. B-cell lymphoma-2 (Bcl-2) family proteins are key to mitochondrial-mediated (or intrinsic) apoptosis [1,4]. The BH3 region of the pro-apoptotic proteins interacts with the canonical ligand binding groove of pro-survival Bcl-2 proteins to neutralize their function [5,6]. This step is crucial to allowing pro-apoptotic Bak and Bax to launch apoptosis by permeabilizing the mitochondrial outer membrane (MOMP) [7,8] to release pro-apoptogenic factors such as cytochrome c from mitochondria that activate the caspase cascade to dismantle the cell [9]

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