Chlorovirus PBCV-1 protein A064R has three of the transferase activities necessary to synthesize its capsid protein N-linked glycans

Immacolata Speciale, Maria Elena Laugieri, Eric Noel, Sicheng Lin, Todd L. Lowary, Antonio Molinaro, Garry A. Duncan, Irina V. Agarkova, Domenico Garozzo, Michela G. Tonetti, James L. van Etten, Cristina de Castro

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


Paramecium bursaria chlorella virus-1 (PBCV-1) is a large double-stranded DNA (dsDNA) virus that infects the unicellular green alga Chlorella variabilis 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 a064r 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 N-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.

Original languageEnglish (US)
Pages (from-to)28735-28742
Number of pages8
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number46
StatePublished - Nov 17 2020


  • Glycosyltransferases | methyltransferases | multi domain protein | chloroviruses | N-glycan

ASJC Scopus subject areas

  • General


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