Abstract
AbstractThe general perception of viruses is that they are small in terms of size and genome, and that they hijack the host machinery to glycosylate their capsid. Giant viruses subvert all these concepts: their particles are not small, and their genome is more complex than that of some bacteria. Regarding glycosylation, this concept has been already challenged by the finding that Chloroviruses have an autonomous glycosylation machinery that produces oligosaccharides similar in size to those of small viruses (6–12 units), albeit different in structure compared to the viral counterparts. We report herein that Mimivirus possesses a glycocalyx made of two different polysaccharides, now challenging the concept that all viruses coat their capsids with oligosaccharides of discrete size. This discovery contradicts the paradigm that such macromolecules are absent in viruses, blurring the boundaries between giant viruses and the cellular world and opening new avenues in the field of viral glycobiology.
Highlights
Glycans, either alone or linked to a carrier, are molecules essential in all the domains of life, and the way they occur has been continuously challenged
The best condition relied on heating at 100 8C the viral particles in the presence of DTT (Figures 1 c–e) for 2 h. This treatment returned bald virions (Figures 1 c,d), with only few damaged while the fibrils were found in the medium as aggregates due to heating (Figure 1 e)
Similar results were obtained by analyzing Mimivirus M4 particles (Figure S1a), a fibril-deficient mutant of Mimivirus (Figure 1 f).[17]
Summary
Either alone or linked to a carrier, are molecules essential in all the domains of life, and the way they occur has been continuously challenged. N-linked glycans were initially thought to be restricted to Eukarya, but it is clear that they are produced by both Bacteria and Archaea, using biosynthetic pathways which share many analogies among all of them, in spite of the different monosaccharide architecture.[1] O-linked glycoproteins have been found to be ubiquitous too, from the small mucins or the huge proteoglycans in animals, to the unusual glycans that decorate the flagellins in Bacteria and the S-layer proteins in Archaea. Concerning viruses, the general view is that they do not encode any of the proteins needed for the glycosylation process. Many viruses, like Ebola,[2] or HIV,[3] decorate their capsid proteins with oligosaccharides of discrete size (6–12 units) entirely synthetized and attached by the host glycosylation machinery. The glycans of these viruses resemble those of the host
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