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The alphavirus E3 glycoprotein functions in a clade-specific manner.

ABSTRACT: The 80 trimeric, glycoprotein spikes that cover the surface of alphavirus particles are required for mediating viral entry into a host cell. Spike assembly is a regulated process that requires interactions between five structural proteins, E3, E2, 6K and its translational frameshift product TF, and E1. E3 is a small, ?65-amino-acid glycoprotein that has two known functions: E3 serves as the signal sequence for translocation of the E3-E2-6K-E1 polyprotein into the endoplasmic reticulum (ER), and cleavage of E3 from E2 is essential for virus maturation. Nonetheless, when E3 is replaced with an ER signal sequence, spikes do not form and infectious particles are not assembled, suggesting an additional role(s) for E3 in the viral life cycle. To further investigate the role of E3 in spike assembly, we made chimeric viruses in which E3 from one alphavirus species is replaced with E3 from another species. Our results demonstrate that when E3 is interchanged between alphavirus species that belong to the same virus clade, viral titers and particle morphologies and compositions are similar to what are observed for the parental virus. In contrast, for chimeras in which E3 is derived from a different clade than the parental virus, we observed reduced titers and the formation of particles with atypical morphologies and protein compositions. We further characterized the E3 chimeras using a combination of structure-function and revertant analyses. This work revealed two specific interactions between E3 and its cognate E2 glycoprotein that are important for regulating spike assembly.

SUBMITTER: Snyder AJ

PROVIDER: S-EPMC3503070 | biostudies-literature | 2012 Dec

REPOSITORIES: biostudies-literature

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The alphavirus E3 glycoprotein functions in a clade-specific manner.

Snyder Anthony J AJ Mukhopadhyay Suchetana S

Journal of virology 20121003 24

The 80 trimeric, glycoprotein spikes that cover the surface of alphavirus particles are required for mediating viral entry into a host cell. Spike assembly is a regulated process that requires interactions between five structural proteins, E3, E2, 6K and its translational frameshift product TF, and E1. E3 is a small, ∼65-amino-acid glycoprotein that has two known functions: E3 serves as the signal sequence for translocation of the E3-E2-6K-E1 polyprotein into the endoplasmic reticulum (ER), and ...[more]

PMID: 23035234

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Project description:Alphaviruses are small enveloped RNA viruses that bud from the host cell plasma membrane. Alphavirus particles have a highly organized structure, with a nucleocapsid core containing the RNA genome surrounded by the capsid protein, and a viral envelope containing 80 spikes, each a trimer of heterodimers of the E1 and E2 glycoproteins. The capsid protein and envelope proteins are both arranged in organized lattices that are linked via the interaction of the E2 cytoplasmic tail/endodomain with the capsid protein. We previously characterized the role of two highly conserved histidine residues, H348 and H352, located in an external, juxtamembrane region of the E2 protein termed the D-loop. Alanine substitutions of H348 and H352 inhibit virus growth by impairing late steps in the assembly/budding of virus particles at the plasma membrane. To investigate this budding defect, we selected for revertants of the E2-H348/352A double mutant. We identified eleven second-site revertants with improved virus growth and mutations in the capsid, E2 and E1 proteins. Multiple isolates contained the mutation E2-T402K in the E2 endodomain or E1-T317I in the E1 ectodomain. Both of these mutations were shown to partially restore H348/352A growth and virus assembly/budding, while neither rescued the decreased thermostability of H348/352A. Within the alphavirus particle, these mutations are positioned to affect the E2-capsid interaction or the E1-mediated intertrimer interactions at the 5-fold axis of symmetry. Together, our results support a model in which the E2 D-loop promotes the formation of the glycoprotein lattice and its interactions with the internal capsid protein lattice.IMPORTANCE Alphaviruses include important human pathogens such as Chikungunya and the encephalitic alphaviruses. There are currently no licensed alphavirus vaccines or effective antiviral therapies, and more molecular information on virus particle structure and function is needed. Here, we highlight the important role of the E2 juxtamembrane D-loop in mediating virus budding and particle production. Our results demonstrated that this E2 region affects both the formation of the external glycoprotein lattice and its interactions with the internal capsid protein shell.

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The alphavirus E3 glycoprotein functions in a clade-specific manner.

Publications

The alphavirus E3 glycoprotein functions in a clade-specific manner.

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