Novel Chloroviruses With Unique Glycans On Their Major Capsid Proteins

Chloroviruses, of the family Phycodnaviridae, are large, dsDNA viruses with a genome of 290 to 410 kb. These virus genomes are so large that they are classified as “giant viruses”. Within this genome, up to 16 tRNAs and 330 to 450 proteins are encoded. Among the massive amounts of genes and proteins are unique carbohydrate synthesis/metabolism genes, which are responsible for the glycosylation of chloroviruses major capsid proteins. In most viruses, these proteins are glycosylated by the host enzymes located in the endoplasmic reticulum. Instead, Chloroviruses encode their own glycosylation machinery; essentially decorating themselves. Furthermore, these chlorovirus glycans are unlike any glycans seen in any other domain of life. Why these viruses go through the trouble of self-glycosylation and the function of the glycan groups is not known, but the forerunning theories including virion stabilization and host attachment. The goal here was to identify more of these unique glycan structures (or possibly new mutant chloroviruses) through polyclonal antibody screening plaque assays for selecting natural chlorovirus mutations in order to gain a better understanding of the genetics and physiology of this phenomena. Some viruses that escape glycan-specific antibodies were identified, and the structures of these glycans are currently being identified by our glycochemist collaborator in Italy. Key Words: Chlorovirus, gene, glycan/glycoprotein, major capsid protein