Date Published: August 5, 2019
Publisher: Public Library of Science
Author(s): Vladimira Horova, Heyrhyoung Lyoo, Bartosz Różycki, Dominika Chalupska, Miroslav Smola, Jana Humpolickova, Jeroen R. P. M. Strating, Frank J. M. van Kuppeveld, Evzen Boura, Martin Klima, George A. Belov.
Enteroviruses, members of the family of picornaviruses, are the most common viral infectious agents in humans causing a broad spectrum of diseases ranging from mild respiratory illnesses to life-threatening infections. To efficiently replicate within the host cell, enteroviruses hijack several host factors, such as ACBD3. ACBD3 facilitates replication of various enterovirus species, however, structural determinants of ACBD3 recruitment to the viral replication sites are poorly understood. Here, we present a structural characterization of the interaction between ACBD3 and the non-structural 3A proteins of four representative enteroviruses (poliovirus, enterovirus A71, enterovirus D68, and rhinovirus B14). In addition, we describe the details of the 3A-3A interaction causing the assembly of the ACBD3-3A heterotetramers and the interaction between the ACBD3-3A complex and the lipid bilayer. Using structure-guided identification of the point mutations disrupting these interactions, we demonstrate their roles in the intracellular localization of these proteins, recruitment of downstream effectors of ACBD3, and facilitation of enterovirus replication. These structures uncovered a striking convergence in the mechanisms of how enteroviruses and kobuviruses, members of a distinct group of picornaviruses that also rely on ACBD3, recruit ACBD3 and its downstream effectors to the sites of viral replication.
Enteroviruses are small RNA viruses that belong to the Enterovirus genus of the Picornaviridae family. They are non-enveloped positive-sense single-stranded RNA viruses with icosahedral capsids, currently consisting of 15 species. Seven enterovirus species (Enterovirus A-D and Rhinovirus A-C) contain human pathogens, such as polioviruses, numbered enteroviruses, echoviruses, coxsackieviruses, and rhinoviruses. They cause a variety of diseases ranging from common cold to acute hemorrhagic conjunctivitis, meningitis, myocarditis, encephalitis, or poliomyelitis . The genome of the enteroviruses encodes the capsid proteins and seven non-structural proteins (named 2A-2C and 3A-3D). The latter carry out many essential processes including genome replication, polyprotein processing, host membrane reorganization, and manipulation of intracellular trafficking. To facilitate these functions, several host factors are recruited to the sites of enterovirus replication through direct or indirect interactions with viral proteins. For instance, the enterovirus non-structural 3A proteins directly bind to the Golgi-specific brefeldin A-resistant guanine nucleotide exchange factor-1 (GBF1)  and acyl-CoA-binding domain-containing protein-3 (ACBD3, also known as GCP60) .
Considering the commonness of enterovirus-mediated infections within human population, it is surprising that no antiviral therapy for enteroviruses has been approved yet. Targeting essential host factors instead of rapidly mutating viral enzymes represents a promising strategy. Several host factors essential for enterovirus replication are recruited to the sites of viral replication by a direct protein-protein interaction between the host factor and a viral protein. A detailed knowledge of the structures of such complexes can open up prospects for a structure-guided development of small chemical compounds targeting these interactions, yielding a novel class of antivirals to combat infections caused by these pathogens.