Viral inosine triphosphatase: A mysterious enzyme with typical activity, but an atypical function.

Amy M James,Andy M Bailey,Susan E Seal,Gary D Foster

doi:10.1111/mpp.13021

Amy M James, Andy M Bailey + Show 2 more

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https://doi.org/10.1111/mpp.13021

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Abstract

Plant viruses typically have highly condensed genomes, yet the plant‐pathogenic viruses Cassava brown streak virus, Ugandan cassava brown streak virus, and Euphorbia ringspot virus are unusual in encoding an enzyme not yet found in any other virus, the “house‐cleaning” enzyme inosine triphosphatase. Inosine triphosphatases (ITPases) are highly conserved enzymes that occur in all kingdoms of life and perform a house‐cleaning function by hydrolysing the noncanonical nucleotide inosine triphosphate to inosine monophosphate. The ITPases encoded by cassava brown streak virus and Ugandan cassava brown streak virus have been characterized biochemically and are shown to have typical ITPase activity. However, their biological role in virus infection has yet to be elucidated. Here we review what is known of viral‐encoded ITPases and speculate on potential roles in infection with the aim of generating a greater understanding of cassava brown streak viruses, a group of the world's most devastating viruses.

Highlights

The study by Tomlinson et al (2019) did find a delayed increase in transcript abundance for mutant viruses lacking Inosine triphosphatases (ITPases) compared to wild-type viruses, which could potentially be a result of reduced translation efficiency of viral proteins involved in viral RNA replication
ITPases are highly conserved across all kingdoms of life and are important enzymes for prevention of mutagenic effects caused by accumulation of noncanonical nucleotides
ITPases have recently been discovered in three plant RNA viruses, but their biological role

Summary

Introduction

As ITPase is highly conserved across all kingdoms of life, it is likely that ITPase in plants shares a important role in the removal of potentially mutagenic noncanonical nucleotides. Plants infected with wild-type UCBSV virus showed a similar phenotype to plants infected with CBSV Ham1 mutant viruses, suggesting the two viruses encode ITPases with different roles in infection; no mutant UCBSV virus was tested so any attenuation of symptoms is unknown (Tomlinson et al, 2019).

Results

Conclusion