Chlorovirus PBCV-1 Multidomain Protein A111/114R Has Three Glycosyltransferase Functions Involved in the Synthesis of Atypical N-Glycans

Authors

Eric Noel, University of Nebraska - LincolnFollow
Anna Notaro, University of Napoli Federico II & Aix-Marseille UniversitéFollow
Immacolata Speciale, University of Napoli Federico IIFollow
Garry A. Duncan, University of Nebraska - LincolnFollow
Cristina De Castro, University of Napoli Federico IIFollow
James L. Van Etten, University of Nebraska - LincolnFollow

ORCID IDs

https://orcid.org/0000-0003-0839-5476

https://orcid.org/0000-0002-7224-8641

https://orcid.org/0000-0003-4363-7450

https://orcid.org/0000-0002-5147-1756

https://orcid.org/0000-0002-5063-0049

Document Type

Article

Date of this Version

2021

Citation

Noel,E.;Notaro,A.; Speciale, I.; Duncan, G.A.; De Castro, C.; Van Etten, J.L. Chlorovirus PBCV-1 Multidomain Protein A111/114R Has Three Glycosyltransferase Functions Involved in the Synthesis of Atypical N-Glycans. Viruses 2021, 13, 87. https://doi.org/10.3390/v13010087

Comments

2021 by the authors.

Abstract

The structures of the four N-linked glycans from the prototype chlorovirus PBCV-1 major capsid protein do not resemble any other glycans in the three domains of life. All known chloroviruses and antigenic variants (or mutants) share a unique conserved central glycan core consisting of five sugars, except for antigenic mutant virus P1L6, which has four of the five sugars. A combination of ge- netic and structural analyses indicates that the protein coded by PBCV-1 gene a111/114r, conserved in all chloroviruses, is a glycosyltransferase with three putative domains of approximately 300 amino acids each. Here, in addition to in silico sequence analysis and protein modeling, we measured the hydrolytic activity of protein A111/114R. The results suggest that domain 1 is a galactosyltransferase, domain 2 is a xylosyltransferase and domain 3 is a fucosyltransferase. Thus, A111/114R is the protein likely responsible for the attachment of three of the five conserved residues of the core region of this complex glycan, and, if biochemically corroborated, it would be the second three-domain protein coded by PBCV-1 that is involved in glycan synthesis. Importantly, these findings provide additional support that the chloroviruses do not use the canonical host endoplasmic reticulum–Golgi glycosyla- tion pathway to glycosylate their glycoproteins; instead, they perform glycosylation independent of cellular organelles using virus-encoded enzymes.