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

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 β-L-rhamnosyltransferase activity, domain 2 has an α -L-rhamnosyltransferase activity and domain 3 is a methyltransferase that decorates two positions in the terminal α -L-rhamnose (Rha) unit. The a075l gene encodes a β -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, α-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. Includes supplemental material

Total synthesis and structural studies of zwitterionic Bacteroides fragilis polysaccharide A1 fragments

Zwitterionic polysaccharides (ZPSs) are exceptional carbohydrates,carrying both positively charged amine groups and negatively chargedcarboxylates, that can be loaded onto MHC-II molecules to activateT cells. It remains enigmatic, however, how these polysaccharidesbind to these receptors, and to understand the structural featuresresponsible for this "peptide-like" behavior, well-definedZPS fragments are required in sufficient quantity and quality. Wehere present the first total synthesis of Bacteroidesfragilis PS A1 fragments encompassing up to 12 monosaccharides,representing three repeating units. Key to our successful syntheseshas been the incorporation of a C-3,C-6-silylidene-bridged "ring-inverted"galactosamine building block that was designed to act as an apt nucleophileas well as a stereoselective glycosyl donor. Our stereoselective synthesisroute is further characterized by a unique protecting group strategy,built on base-labile protecting groups, which has allowed the incorporationof an orthogonal alkyne functionalization handle. Detailed structuralstudies have revealed that the assembled oligosaccharides take upa bent structure, which translates into a left-handed helix for largerPS A1 polysaccharides, presenting the key positively charged aminogroups to the outside of the helix. The availability of the fragmentsand the insight into their secondary structure will enable detailedinteraction studies with binding proteins to unravel the mode of actionof these unique oligosaccharides at the atomic level.Bio-organic Synthesi

Osservatorio previsionale sul mercato italiano delle macchine per la meccanizzazione agricola. Assemblea generale. Giugno 2003

Consiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7, Rome / CNR - Consiglio Nazionale delle RichercheSIGLEITItal

Osservatorio previsionale sul mercato italiano delle macchine per la meccanizzazione agricola. Assemblea generale. Giugno 2000

Consiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7, Rome / CNR - Consiglio Nazionale delle RichercheSIGLEITItal

Osservatorio previsionale sul mercato italiano ed europeo delle macchine per la meccanizzazione agricola. Assemblea generale. Giugno 2002

Consiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7, Rome / CNR - Consiglio Nazionale delle RichercheSIGLEITItal

gem-Difluorocarbadisaccharides: Restoring the exo-Anomeric Effect

International audienceMolecular mimicry is an essential part of the development of drugs and molecular probes. In the chemical glycobiology field, although many glycomimetics have been developed in the past years, it has been considered that many failures in their use are related to the lack of the anomeric effects in these analogues. Additionally, the origin of the anomeric effects is still the subject of virulent scientific debates. Herein, by combining chemical synthesis, NMR methods, and theoretical calculations, we show that it is possible to restore the anomeric effect for an acetal when replacing one of the oxygen atoms by a CF2 group. This result provides key findings in chemical sciences. On the one hand, it strongly suggests the key relevance of the stereoelectronic component of the anomeric effect. On the other hand, the CF2 analogue adopts the natural glycoside conformation, which might provide new avenues for sugar-based drug design. Molecular mimicry is an essential part of the development of drugs and molecular probes. In the chemical glycobiology field, although many glycomimetics have been developed in the past years, it has been considered that many failures in their use are related to the lack of the anomeric effects in these analogues. Additionally, the origin of the anomeric effects is still the subject of virulent scientific debates. Herein, by combining chemical synthesis, NMR methods, and theoretical calculations, we show that it is possible to restore the anomeric effect for an acetal when replacing one of the oxygen atoms by a CF2 group. This result provides key findings in chemical sciences. On the one hand, it strongly suggests the key relevance of the stereoelectronic component of the anomeric effect. On the other hand, the CF2 analogue adopts the natural glycoside conformation, which might provide new avenues for sugar-based drug design