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Comparative Analysis of Zika Viral Proteins in the Inhibition of Interferon Signaling

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posted on 17.08.2020 by Ling Ling Ng
Abstract
Zika virus belongs to the family of Flaviridae. The virus was first isolated in 1947 in monkeys of Zika forest in Uganda. Human infection by Zika virus was first reported in 1952. Since then, only about twenty additional human cases have been documented till 2006, and yet no or mild symptoms were observed in these patients. The virus was initially confined in Africa and Asia, until the first outbreak in Yap Islands in the southwestern Pacific Ocean in 2007, where patients infected by the Asia-lineage Zika virus showed symptoms including conjunctivitis and rashes. In 2015-2016, Zika virus of the same lineage caused a major epidemic in the Americas. An estimate of 1.5 million people in Brazil were infected by Zika virus. More importantly, previously un-observed neurological symptoms including severe birth defects, such as microcephaly in new-born babies, and Guillain-Barré syndrome in adults were displayed by infected patients. In the past three years, investigation on the genetic differences between the original African strains and the current circulating Asian strains has been performed by many groups to study their causation to distinctive pathophysiological outcomes and enhanced human-to-human transmission. Type I interferon response of the host is the first-line defence mechanism against infections. Nevertheless, the differential dysregulation of this host signalling pathway by the two Zika virus lineages has not been fully characterized. Therefore, in this study we will compare the ability of individual Zika virus proteins from the two lineages in antagonizing the host Type I interferon response.

In this study, we first performed phylogenetic analysis and amino acid alignment to determine the amino acid differences of more than 600 African and non-African Zika virus sequences. 20 representative sequences of African and Asian strains were selected and aligned for the identification of the conserved substitutions. It encodes a single polyprotein that is proteolytically cleaved into three structural proteins (C, E, M) and seven non-structural proteins (NS1, 2A, 2B, 3, 4A, 4B, 5). The alignment results showed that NS5 has the largest number of amino acid substitutions. In addition, to study the interferon antagonistic properties of structural and non-structural proteins of the African and Asian Zika virus, we generated expression vectors for individual viral proteins of MR766 (African strain/Uganda/1947) and PRVABC-59 (Asian strain/Puerto Rico/2015) strains. Using dual luciferase reporter system, we showed that structural proteins had less suppressive effect on type I interferon signalling, while non-structural proteins inhibited IFNβ, ISRE, IRF3 and NFκB to different extends. Moreover, non-structural proteins mainly suppressed the RIG-I induced IFNβ activity. On the other hand, NS5 has the greatest inhibitory effect on RIG-I induced type I interferon signalling among all Zika virus-encoded proteins.
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