title: Giant virus Megavirus chilensis encodes the biosynthetic pathway for uncommon acetamido sugars.
abstract: Giant viruses mimicking microbes, by the sizes of their particles and the heavily glycosylated fibrils surrounding their capsids, infect Acanthamoeba sp., which are ubiquitous unicellular eukaryotes. The glycans on fibrils are produced by virally encoded enzymes, organized in gene clusters. Like Mimivirus, Megavirus glycans are mainly composed of virally synthesized N-acetylglucosamine (GlcNAc). They also contain N-acetylrhamnosamine (RhaNAc), a rare sugar; the enzymes involved in its synthesis are encoded by a gene cluster specific to Megavirus close relatives. We combined activity assays on two enzymes of the pathway with mass spectrometry and NMR studies to characterize their specificities. Mg534 is a 4,6-dehydratase 5-epimerase; its three-dimensional structure suggests that it belongs to a third subfamily of inverting dehydratases. Mg535, next in the pathway, is a bifunctional 3-epimerase 4-reductase. The sequential activity of the two enzymes leads to the formation of UDP-l-RhaNAc. This study is another example of giant viruses performing their glycan synthesis using enzymes different from their cellular counterparts, raising again the question of the origin of these pathways.
authors.affiliation: From the Department of Experimental Medicine and Center of Excellence for Biomedical Research, University of Genova, Viale Benedetto XV,1 16132 Genova, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Piacente
authors.affiliation: the Department of Chemical Sciences, University of Napoli "Federico II", Via Cintia 4, Italy.
authors.forename: Cristina
authors.initials: C
authors.lastname: De Castro
authors.affiliation: the Structural and Genomic Information Laboratory, CNRS, Aix-Marseille Université UMR7256, IMM, Parc Scientifique de Luminy, FR-13288 Marseille, France, and.
authors.forename: Sandra
authors.initials: S
authors.lastname: Jeudy
authors.affiliation: the Department of Chemical Sciences, University of Napoli "Federico II", Via Cintia 4, Italy.
authors.forename: Antonio
authors.initials: A
authors.lastname: Molinaro
authors.affiliation: From the Department of Experimental Medicine and Center of Excellence for Biomedical Research, University of Genova, Viale Benedetto XV,1 16132 Genova, Italy, the Department of Hearth Environmental and Life Science (DISTAV), University of Genova, Corso Europa 26, 16132 Genova, Italy.
authors.forename: Annalisa
authors.initials: A
authors.lastname: Salis
authors.affiliation: From the Department of Experimental Medicine and Center of Excellence for Biomedical Research, University of Genova, Viale Benedetto XV,1 16132 Genova, Italy.
authors.forename: Gianluca
authors.initials: G
authors.lastname: Damonte
authors.affiliation: From the Department of Experimental Medicine and Center of Excellence for Biomedical Research, University of Genova, Viale Benedetto XV,1 16132 Genova, Italy.
authors.forename: Cinzia
authors.initials: C
authors.lastname: Bernardi
authors.affiliation: the Structural and Genomic Information Laboratory, CNRS, Aix-Marseille Université UMR7256, IMM, Parc Scientifique de Luminy, FR-13288 Marseille, France, and Chantal.Abergel@igs.cnrs-mrs.fr.
authors.forename: Chantal
authors.initials: C
authors.lastname: Abergel
authors.affiliation: From the Department of Experimental Medicine and Center of Excellence for Biomedical Research, University of Genova, Viale Benedetto XV,1 16132 Genova, Italy, tonetti@unige.it.
authors.forename: Michela G
authors.initials: MG
authors.lastname: Tonetti
mesh_terms: D000595:Amino Acid Sequence; D053898:Biosynthetic Pathways; D002241:Carbohydrates / Q000096:biosynthesis* / Q000737:chemistry; D004267:DNA Viruses / Q000235:genetics* / Q000378:metabolism; D016679:Genome, Viral; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid
chemical_list: D002241:Carbohydrates
keywords: Carbohydrate Metabolism; Gas Chromatography-Mass Spectrometry (GC-MS); Glycosylation; Mass Spectrometry (MS); Megavirus Chilensis; N-Acetyl-L-Rhamnosamine; Nuclear Magnetic Resonance (NMR); UDP-N-acetylglucosamine; Virus Structure