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Structural and functional insights into alphavirus polyprotein processing and pathogenesis.

ABSTRACT: Alphaviruses, a group of positive-sense RNA viruses, are globally distributed arboviruses capable of causing rash, arthritis, encephalitis, and death in humans. The viral replication machinery consists of four nonstructural proteins (nsP1-4) produced as a single polyprotein. Processing of the polyprotein occurs in a highly regulated manner, with cleavage at the P2/3 junction influencing RNA template use during genome replication. Here, we report the structure of P23 in a precleavage form. The proteins form an extensive interface and nsP3 creates a ring structure that encircles nsP2. The P2/3 cleavage site is located at the base of a narrow cleft and is not readily accessible, suggesting a highly regulated cleavage. The nsP2 protease active site is over 40 Å away from the P2/3 cleavage site, supporting a trans cleavage mechanism. nsP3 contains a previously uncharacterized protein fold with a zinc-coordination site. Known mutations in nsP2 that result in formation of noncytopathic viruses or a temperature sensitive phenotype cluster at the nsP2/nsP3 interface. Structure-based mutations in nsP3 opposite the location of the nsP2 noncytopathic mutations prevent efficient cleavage of P23, affect RNA infectivity, and alter viral RNA production levels, highlighting the importance of the nsP2/nsP3 interaction in pathogenesis. A potential RNA-binding surface, spanning both nsP2 and nsP3, is proposed based on the location of ion-binding sites and adaptive mutations. These results offer unexpected insights into viral protein processing and pathogenesis that may be applicable to other polyprotein-encoding viruses such as HIV, hepatitis C virus (HCV), and Dengue virus.

SUBMITTER: Shin G

PROVIDER: S-EPMC3478664 | biostudies-literature | 2012 Oct

REPOSITORIES: biostudies-literature

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Structural and functional insights into alphavirus polyprotein processing and pathogenesis.

Shin Gyehwa G Yost Samantha A SA Miller Matthew T MT Elrod Elizabeth J EJ Grakoui Arash A Marcotrigiano Joseph J

Proceedings of the National Academy of Sciences of the United States of America 20120925 41

Alphaviruses, a group of positive-sense RNA viruses, are globally distributed arboviruses capable of causing rash, arthritis, encephalitis, and death in humans. The viral replication machinery consists of four nonstructural proteins (nsP1-4) produced as a single polyprotein. Processing of the polyprotein occurs in a highly regulated manner, with cleavage at the P2/3 junction influencing RNA template use during genome replication. Here, we report the structure of P23 in a precleavage form. The pr ...[more]

PMID: 23010928

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Project description:Burkitt lymphoma (BL) can often be cured by intensive chemotherapy, but the toxicity of such therapy precludes its use in the elderly and in patients with endemic BL (eBL) in developing countries, necessitating new strategies. The normal germinal center B cell is the presumed cell of origin for both BL and diffuse large B cell lymphoma (DLBCL), yet gene expression analysis suggests that these malignancies may utilize different oncogenic pathways. BL is subdivided into a sporadic subtype (sBL) that is diagnosed in developed countries, the EBV-associated eBL subtype, and an HIV-associated subtype (hivBL), but it is unclear whether these subtypes employ similar or divergent oncogenic mechanisms. Here we used high throughput RNA sequencing and RNA interference screening to discover essential regulatory pathways that cooperate with MYC, the defining oncogene of this cancer. In 70% of sBL cases, mutations affecting the transcription factor TCF3 (E2A) or its negative regulator ID3 fostered TCF3 dependency. TCF3 activated the pro-survival PI(3) kinase pathway in BL, in part by augmenting tonic B cell receptor signaling. In 38% of sBL cases, oncogenic CCND3 mutations produced highly stable cyclin D3 isoforms that drive cell cycle progression. These findings suggest opportunities to improve therapy for patients with BL. Gene expression was analyzed using Agilent human 4X44K oligo gene expression arrays. Cell lines (Namalwa, BL41, Daudi, Defauw, and THOMAS) were infected with control (empty vector, Cy3) paired with ID3 (Cy5) or control (shControl, Cy3) paired with shTCF3 (Cy5) constructs, and changes in gene expression were monitored over time after induction of the constructs with doxycyclin. In Namalwa (n=8) and THOMAS (n=4) cell lines, a four timepoint series (24, 48, 72, 96 hours) of construct induction was analyzed, for a total of 12 arrays. In BL41 (n=4), Daudi (n=4) and Defauw (n=4) cell lines, a two timepoint series (24 and 48 hours) of construct induction was analyzed, for a total of 12 arrays. In addition, two cell lines (Daudi and THOMAS) were treated with Rapamycin (100 pM) and paired with a DMSO control in a four timepoint series (3, 6, 12 and 24 hours) for a total of 8 arrays.

Dataset Information

Structural and functional insights into alphavirus polyprotein processing and pathogenesis.

Publications

Structural and functional insights into alphavirus polyprotein processing and pathogenesis.

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