Structure of the herpes simplex virus 1 capsid with associated tegument protein complexes

Abstract

INTRODUCTION Since Hippocrates first described the cutaneous spreading of herpes simplex lesions, many other diseases—chickenpox, infectious mononucleosis, nasopharyngeal carcinoma, and Kaposi’s sarcoma—have been found to be associated with the nine known human herpesviruses. Among them, herpes simplex virus type 1 (HSV-1, causes cold sores), type 2 (HSV-2, causes genital herpes), and varicella-zoster virus (causes chickenpox and shingles)—which all belong to the α-herpesvirus subfamily—can establish lifelong latent infection within our peripheral nervous system. RATIONALE A prominent feature of these neurotropic viruses is the long-range (up to tens of centimeters) axonal retrograde transport of the DNA-containing viral capsid from nerve endings at sites of infection (such as the lips) to neuronal cell bodies at the ganglia to establish latency or, upon reactivation, anterograde transport of the progeny viral particles from the ganglia to nerve terminals, resulting in reinfection of the dermis. Capsid-associated tegument complexes (CATCs) have been demonstrated to be involved in this cytoskeleton-dependent capsid transport. Because of the large size (~1300 Å) of HSV-1 particles, it has been difficult to obtain atomic structures of the HSV-1 capsid and CATC; consequently, the structural bases underlying α-herpesviruses’ remarkable capability of long-range neuronal transport and many other aspects of its life cycle are poorly understood. RESULTS By using cryo–electron microscopy, we obtained an atomic model of the HSV-1 capsid with CATC, comprising multiple conformers of the capsid proteins VP5, VP19c, VP23, and VP26 and tegument proteins pUL17, pUL25, and pUL36. Crowning every capsid vertex are five copies of heteropentameric CATC. The pUL17 monomer in each CATC bridges over triplexes Ta and Tc on the capsid surface and supports a coiled-coil helix bundle of a pUL25 dimer and a pUL36 dimer, thus positioning their flexible domains for potential involvement in nuclear egress and axonal transport of the capsid. The single C-terminal helix of pUL36 resolved in the CATC links the capsid to the outer tegument and envelope: As the largest tegument protein in all herpesviruses and essential for virion formation, pUL36 has been shown to interact extensively with other tegument proteins, which in turn interact with envelope glycoproteins. Architectural similarities between herpesvirus triplex proteins and auxiliary cementing protein gpD in bacteriophage λ, in addition to the bacteriophage HK97 gp5–like folds in their major capsid proteins and structural similarities in their DNA packaging and delivery apparatuses, indicate that the commonality between bacteriophages and herpes-viruses extends to their auxiliary components. Notwithstanding this broad evolutionary conservation, comparison of HSV-1 capsid proteins with those of other herpesviruses revealed extraordinary structural diversities in the forms of domain insertion and conformation polymorphism, not only for tegument interactions but also for DNA encapsulation...

Structures of three actinobacteriophage capsids: Roles of symmetry and accessory proteins

“…The structure of Myrna shows how common the T=16 capsid architecture is, with examples of viruses found in all domains of life that have a similar structure, for example the human virus HSV-1 [32]. This is the first time it has been described in the Actinobacteria, and suggests that this capsid architecture is adaptable to a number of different hosts and environments to encapsulate large genomes.…”

“…Myrna shows T=16 capsid organization, with a minor capsid protein that sits in hexavalent positions. Following the new framework it is a Tt (4,0) = 64/3, similar to HSV-1 [32]. The interior capsid diameter is 81.1 nm.…”

In situstructure determination of virus capsids imaged within cell nuclei by correlative light and cryo-electron tomography

“…The precise site of pUL36 addition to the capsids, in the nucleus or in the cytoplasm, has been the subject of much debate, with the balance of evidence suggesting that it binds capsids in the cytoplasm 20,21 . This is at odds with structural data that show two copies of pUL36 intimately associated with pUL17 and pUL25 to form a 5-helix bundle in the CATC 19 .…”

“…S2). In recent high-resolution single particle reconstructions of capsids within purified HSV-1 virions, the pentaskelion structure can be clearly seen above the penton vertices and has been attributed to the proteins pUL17, pUL25 and pUL36 16,19 .…”

“…In the cytoplasm, nucleocapsids become surrounded by a dense proteinaceous layer known as the tegument, before budding into plasma membrane derived endocytic membranes; giving rise to mature enveloped virions 17,18 . The nucleocapsid structure has been extensively studied and was recently characterised at high resolution, leading to an atomistic model of this large (1250Å diameter) and complex assembly 19 . Of particular relevance to this study is the definition of the structure and composition of an assembly variously known as the capsid-vertex specific component (CVSC) or capsid associated tegument complex (CATC).…”