AI Article Synopsis

  • Chlorella virus-1 (PBCV-1) is a large dsDNA virus that infects a single-celled green alga and uniquely encodes enzymes for synthesizing its capsid protein’s glycans, which have distinct structures compared to those found in other life forms.
  • Research on PBCV-1 mutations indicated the presence of a glycosyltransferase (GT) with three distinct functional domains: one for β-l-rhamnosyltransferase, one resembling bacterial proteins, and one for methylating rhamnose units.
  • This study identifies two glycosyltransferase activities linked to the viral capsid protein glycan synthesis and shows that one viral protein, A

Article Abstract

chlorella virus-1 (PBCV-1) is a large double-stranded DNA (dsDNA) virus that infects the unicellular green alga NC64A. Unlike many other viruses, PBCV-1 encodes most, if not all, of the enzymes involved in the synthesis of the glycans attached to its major capsid protein. Importantly, these glycans differ from those reported from the three domains of life in terms of structure and asparagine location in the sequon of the protein. Previous data collected from 20 PBCV-1 spontaneous mutants (or antigenic variants) suggested that the gene encodes a glycosyltransferase (GT) with three domains, each with a different function. Here, we demonstrate that: domain 1 is a β-l-rhamnosyltransferase; domain 2 is an α-l-rhamnosyltransferase resembling only bacterial proteins of unknown function, and domain 3 is a methyltransferase that methylates the C-2 hydroxyl group of the terminal α-l-rhamnose (Rha) unit. We also establish that methylation of the C-3 hydroxyl group of the terminal α-l-Rha is achieved by another virus-encoded protein A061L, which requires an O-2 methylated substrate. This study, thus, identifies two of the glycosyltransferase activities involved in the synthesis of the -glycan of the viral major capsid protein in PBCV-1 and establishes that a single protein A064R possesses the three activities needed to synthetize the 2-OMe-α-l-Rha-(1→2)-β-l-Rha fragment. Remarkably, this fragment can be attached to any xylose unit.

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7682578PMC
http://dx.doi.org/10.1073/pnas.2016626117DOI Listing

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