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标题：Chlorovirus PBCV-1 protein A064R has three of the transferase activities necessary to synthesize its capsid protein N-linked glycans
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作者：Immacolata Speciale ; Maria Elena Laugieri ; Eric Noel 等
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2020
卷号：117
期号：46
页码：28735-28742
DOI：10.1073/pnas.2016626117
出版社：The National Academy of Sciences of the United States of America
摘要：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.
关键词：glycosyltransferases ; methyltransferases ; multi domain protein ; chloroviruses ; N-glycan