The chlorovirus Paramecium bursaria chlorella virus 1 (PBCV-1), is a large dsDNA virus that infects the microalgae Chlorella variabilis NC64A.[1] It is a member of the giant virus group, a class of viruses that differ from the others in shape, genome size and number of encoded proteins.[2] It’s main feature is that unlike to other viruses, PBCV-1 encodes most, if not all, of the components required to glycosylate its major capsid protein (MCP), named Vp54 (gene a430l).[3] Noteworthy, Vp54 is decorated with four glycans, that are different from all other N-glycans known so far in the three domains of the life.[4]
Recent analysis about the PBCV-1 gene, has disclosed that it encodes, at least, six putative glycosyltransferases[1], presumably involved in glycosylation of the its major capsid protein Vp54. One of them, the A064R, catched our attention because 18 of 21 antigenic variants of PBCV-1 present mutations in this gene or it was deleted.[5] Comparing the wild-type glycan structures from PBCV-1 with those from a set of PBCV-1 mutants, that have truncated glycan structures, it was possible to address the role of the whole a064r gene. This gene encodes a protein of 638 amino acids organized in three domains [4], each with a particular function.
Combining structural analyses with enzymatic reactions, it is now established that the domain 1 encodes for a β-(1,4)-L-rhamnosyl transferase onto a xylose acceptor,[5] in contrast with previous data, which supposed that such domain encoded for a glucosyl-transferase.[6]
Domain 2 has no resemblance with any known glycosyltransferase, and it encodes for a α-(1,2)-L-rhamnosyl transferase that recognizes rhamnose as acceptor, while domain 3 has a double methyltransferase activity and acts on a terminal rhamnose unit.
This communication will present the strategy used to evaluate the activity of this complex protein.
- Van Etten, JL, Agarkova, I, Dunigan, DD, Tonetti, M, De Castro, C, Duncan, GA. Viruses, 2017, 9:88
- De Castro, C, Duncan, GA, Garozzo, D, Molinaro, A, Sturiale, L, Tonetti, M, Van Etten, JL. Glycobiophysics. Advances in Experimental Medicine and Biology, 2018, vol. 1104:237-257. Springer, Singapore
- Van Etten, JL, Gurnon, J, Yanai-Balser, G, Dunigan, D, Graves, MV. Biochem Biophys Acta, 2010, 1800 (2):152-159
- De Castro, C, Molinaro, A, Piacente, F, Gurnon, JR, Sturiale, L, Palmigiano, A, Lanzetta, R, Parrilli, M, Garozzo, D, Tonetti, MG, Van Etten, JL. PNAS, 2013 110: 13956-13960.
- Speciale, I, Duncan, GA, Unione, L, Agarkova, I, Garozzo, D, Barbero, JJ, Lin, S, Lowary, TL, Molinaro, A, Noel, E, Laugieri, ME, Tonetti, MG, Van Etten, JL, De Castro, C. JBC, 2019, doi/10.1074/jbc.RA118.007182
- Zhang, Y, Xiang, Y, Van Etten, JL, Rossmann, MG. NIH Public Access, 2007, 15(9): 1031-1039