The chlorovirus Paramecium bursaria chlorella virus 1 (PBCV-1) is a large dsDNA virus that infects the microalga Chlorella variabilis NC64A. Unlike most other viruses, PBCV-1 encodes most, if not all, of the machinery required to glycosylate its major capsid protein (MCP). The structures of the four N-linked glycans from the PBCV-1 MCP consist of nonasaccharides, and similar glycans are not found elsewhere in the three domains of life. Here, we identified the roles of three virus-encoded glycosyltransferases (GTs) that have four distinct GT activities in glycan synthesis. Two of the three GTs were previously annotated as GTs but the third GT was identified in this study. We determined the GT functions by comparing the wild-type glycan structures from PBCV-1 with those from a set of PBCV-1 spontaneous GT genes mutants resulting in antigenic variants having truncated glycan structures. According to our working model, the virus gene a064r encodes a GT with three domains: domain 1 has a -L-rhamnosyltransferase activity, domain 2 has an -L-rhamnosyltransferase activity and domain 3 is a methyltransferase that decorates two positions in the terminal -L-rhamnose (Rha) unit. The a075l gene encodes a -xylosyltransferase that attaches the distal D-xylose (Xyl) unit to the L-fucose (Fuc) that is part of the conserved N-glycan core region. Lastly, gene a071r encodes a GT that is involved in the attachment of a semiconserved element, -D-Rha, to the same L-Fuc in the core region. Our results uncover GT activities that assemble four of the nine residues of the PBCV-1 MCP N-glycans.

The N-glycan structures of the antigenic variants of chlorovirus PBCV-1 major capsid protein help to identify the virus-encoded glycosyltransferases / Speciale, Immacolata; Duncan, Garry A.; Unione, Luca; Agarkova, Irina V.; Garozzo, Domenico; Jimenez-Barbero, Jesus; Lin, Sicheng; Lowary, Todd L.; Molinaro, Antonio; Noel, Eric; Laugieri, Maria Elena; Tonetti, Michela G.; Van Etten, James L.; De Castro, Cristina. - In: THE JOURNAL OF BIOLOGICAL CHEMISTRY. - ISSN 0021-9258. - 294:14(2019), pp. 5688-5699. [10.1074/jbc.RA118.007182]

The N-glycan structures of the antigenic variants of chlorovirus PBCV-1 major capsid protein help to identify the virus-encoded glycosyltransferases

Speciale, Immacolata
Membro del Collaboration Group
;
Molinaro, Antonio
Membro del Collaboration Group
;
De Castro, Cristina
Writing – Review & Editing
2019

Abstract

The chlorovirus Paramecium bursaria chlorella virus 1 (PBCV-1) is a large dsDNA virus that infects the microalga Chlorella variabilis NC64A. Unlike most other viruses, PBCV-1 encodes most, if not all, of the machinery required to glycosylate its major capsid protein (MCP). The structures of the four N-linked glycans from the PBCV-1 MCP consist of nonasaccharides, and similar glycans are not found elsewhere in the three domains of life. Here, we identified the roles of three virus-encoded glycosyltransferases (GTs) that have four distinct GT activities in glycan synthesis. Two of the three GTs were previously annotated as GTs but the third GT was identified in this study. We determined the GT functions by comparing the wild-type glycan structures from PBCV-1 with those from a set of PBCV-1 spontaneous GT genes mutants resulting in antigenic variants having truncated glycan structures. According to our working model, the virus gene a064r encodes a GT with three domains: domain 1 has a -L-rhamnosyltransferase activity, domain 2 has an -L-rhamnosyltransferase activity and domain 3 is a methyltransferase that decorates two positions in the terminal -L-rhamnose (Rha) unit. The a075l gene encodes a -xylosyltransferase that attaches the distal D-xylose (Xyl) unit to the L-fucose (Fuc) that is part of the conserved N-glycan core region. Lastly, gene a071r encodes a GT that is involved in the attachment of a semiconserved element, -D-Rha, to the same L-Fuc in the core region. Our results uncover GT activities that assemble four of the nine residues of the PBCV-1 MCP N-glycans.
2019
The N-glycan structures of the antigenic variants of chlorovirus PBCV-1 major capsid protein help to identify the virus-encoded glycosyltransferases / Speciale, Immacolata; Duncan, Garry A.; Unione, Luca; Agarkova, Irina V.; Garozzo, Domenico; Jimenez-Barbero, Jesus; Lin, Sicheng; Lowary, Todd L.; Molinaro, Antonio; Noel, Eric; Laugieri, Maria Elena; Tonetti, Michela G.; Van Etten, James L.; De Castro, Cristina. - In: THE JOURNAL OF BIOLOGICAL CHEMISTRY. - ISSN 0021-9258. - 294:14(2019), pp. 5688-5699. [10.1074/jbc.RA118.007182]
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11588/752435
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