2.7 Å Cryo-Em Structure of Rotavirus Core Protein VP3, a Unique Capping Machine With a Helicase Activity

Authors

Dilip Kumar
Xinzhe Yu
Sue E Crawford
Rodolfo Moreno
Joanita Jakana
Banumathi Sankaran
Ramakrishnan Anish
Soni Kaundal
Liya Hu
Mary K Estes
Zhao Wang
B V Venkataram Prasad

Publication Date

4-1-2020

Journal

Science Advances

DOI

10.1126/sciadv.aay6410

PMID

32494598

PMCID

PMC7159914

PubMedCentral® Posted Date

4-15-2020

PubMedCentral® Full Text Version

Post-print

Published Open-Access

yes

Keywords

Capsid Proteins, Cryoelectron Microscopy, Genome, Viral, Nucleotidyltransferases, RNA, Viral, Rotavirus, Virion

Abstract

In many viruses, including rotavirus (RV), the major pathogen of infantile gastroenteritis, capping of viral messenger RNAs is a pivotal step for efficient translation of the viral genome. In RV, VP3 caps the nascent transcripts synthesized from the genomic dsRNA segments by the RV polymerase VP1 within the particle core. Here, from cryo-electron microscopy, x-ray crystallography, and biochemical analyses, we show that VP3 forms a stable tetrameric assembly with each subunit having a modular domain organization, which uniquely integrates five distinct enzymatic steps required for capping the transcripts. In addition to the previously known guanylyl- and methyltransferase activities, we show that VP3 exhibits hitherto unsuspected RNA triphosphatase activity necessary for initiating transcript capping and RNA helicase activity likely required for separating the RNA duplex formed transiently during endogenous transcription. From our studies, we propose a new mechanism for how VP3 inside the virion core caps the nascent transcripts exiting from the polymerase.

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