Paramecium bursaria Chlorella virus 1 encodes two enzymes involved in the biosynthesis of GDP-L-fucose and GDP-D-rhamnose.
At least three structural proteins in Paramecium bursaria Chlorella virus (PBCV-1) are glycosylated, including the major capsid protein Vp54. However, unlike other glycoprotein-containing viruses that use host-encoded enzymes in the endoplasmic reticulum-Golgi to glycosylate their proteins, PBCV-1 encodes at least many, if not all, of the glycosyltransferases used to glycosylate its structural proteins. As described here, PBCV-1 also encodes two open reading frames that resemble bacterial and mammalian enzymes involved in de novo GDP-L-fucose biosynthesis. This pathway, starting from GDP-D-mannose, consists of two sequential steps catalyzed by GDP-D-mannose 4,6 dehydratase (GMD) and GDP-4-keto-6-deoxy-D-mannose epimerase/reductase, respectively. The two PBCV-1-encoded genes were expressed in Escherichia coli, and the recombinant proteins had the predicted enzyme activity. However, in addition to the dehydratase activity, PBCV-1 GMD also had a reductase activity, producing GDP-D-rhamnose. In vivo studies established that PBCV-1 GMD and GDP-4-keto-6-deoxy-D-mannose epimerase/reductase are expressed after virus infection and that both GDP-L-fucose and GDP-D-rhamnose are produced in virus-infected cells. Thus, PBCV-1 is the first virus known to encode enzymes involved in nucleotide sugar metabolism. Because fucose and rhamnose are components of the glycans attached to Vp54, the pathway could circumvent a limited supply of GDP sugars by the algal host.
Tonetti
Michela
M
Department of Experimental Medicine, Section of Biochemistry and Center of Excellence for Biomedical Research, University of Genoa, Viale Benedetto XV 1, 16132 Genoa, Italy. tonetti@unige.it
Zanardi
Davide
D
Gurnon
James R
JR
Fruscione
Floriana
F
Armirotti
Andrea
A
Damonte
Gianluca
G
Sturla
Laura
L
De Flora
Antonio
A
Van Etten
James L
JL
D000818:Animals; D000838:Anions; D015152:Blotting, Northern; D002708:Chlorella / Q000235:genetics* / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D002852:Chromatography, Ion Exchange; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000378:metabolism; D008401:Gas Chromatography-Mass Spectrometry; D016679:Genome, Viral; D006154:Guanosine Diphosphate Fucose / Q000096:biosynthesis*; D006156:Guanosine Diphosphate Sugars / Q000096:biosynthesis*; D007700:Kinetics; D008956:Models, Chemical; D008969:Molecular Sequence Data; D009005:Monosaccharides / Q000737:chemistry; D016366:Open Reading Frames; D010247:Paramecium / Q000821:virology*; D011994:Recombinant Proteins / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization; D013997:Time Factors
D000838:Anions; C422949:GDP-rhamnose; D006156:Guanosine Diphosphate Sugars; D009005:Monosaccharides; D011994:Recombinant Proteins; D006154:Guanosine Diphosphate Fucose