Chloroviruses Display an Unprecedented Pattern of N-Glycosylation

N-glycosylation is a fundamental modification of proteins and exists in the three domains of life and in some viruses, including the chloroviruses, Chloroviruses (family Phycodnaviridae) infect eukaryotic encode most, if not all, of the machinery to glycosylate their major capsid proteins. This genus includes large (190 nm in diameter) icosahedral, plaque-forming viruses with an internal lipid membrane and dsDNA genomes encoding as many as 400 proteins.

A new type of core N-glycan common to all chloroviruses has been found. The core element is a pentasaccharide with a β-glucose linked to an asparagine residue which is not located in the typical sequon N-X-T/S. The glucose is linked to a terminal xylose unit and a hyperbranched fucose, which is in turn substituted with a terminal galactose and a second xylose residue. The third position of the fucose unit is always linked to a rhamnose, which is a semiconserved element because its absolute configuration is virus-dependent. Additional decorations occur on this core N-glycan and represent a molecular signature for each chlorovirus.