Chlorovirus PBCV-1 protein A064R has three of the transferase activities necessary to synthesize its capsid protein N-linked glycans
Immacolata Speciale, Maria Elena Laugieri, Eric A. Noel, Sicheng Lin, Todd L. Lowary, Antonio Molinaro, Garry A. Duncan, Irina V. Agarkova, Domenico Garozzo, Michela Tonetti, James L. Van Etten, Cristina De Castro
Abstract
Significance The chloroviruses are unusual because they are predicted to encode most, if not all, of the machinery to synthesize the glycans attached to their major capsid proteins. Here we show that two of the virus-encoded proteins A064R and A061L are functionally active. A064R has three domains: The first two are GTs and the third domain is a methyltransferase. A061L has a methyltransferase activity. The action of these two enzymes produce the fragment 2,3-di-O-methyl-α- l -Rha-(1→2)-β- l -Rha, which is part of the complex N-linked glycan attached to the virus capsid protein. A064R domain 2 is a member of a new GT family. This provides direct evidence that the synthesis of PBCV-1 glycans are accomplished with virus-encoded enzymes.