Identification of Three Novel O-Linked Glycans in the Envelope Protein of Tick-Borne Encephalitis Virus

Tick-borne encephalitis virus is a pathogen endemic to northern Europe and Asia, transmitted through bites from infected ticks. It is a member of the Flaviviridae family, possesses a positive-sense, single-stranded RNA genome encoding a polypeptide that is processed into seven non-structural and three structural proteins, including the envelope (E) protein. The glycosylation of the E protein, a single N-linked glycan at position N154, plays a critical role in viral infectivity and pathogenesis. Here, we dissected the entire glycosylation profile of the E protein using liquid chromatography tandem mass spectrometry and identified three novel O-linked glycans which were found at relatively low frequency. One of the O-linked glycans was positioned close to the highly conserved N-linked glycan site and structural analysis indicated that it may be of relevance for viral maturation. The N154 site was found to be glycosylated with a high frequency, containing oligomannose or complex-type structures, some of which are fucosylated. An unusually high portion of oligomannose N-linked glycan structures exhibited compositions that are normally observed on proteins while they are translocated from the endoplasmic reticulum to the trans golgi network, suggesting disruption of the glycan processing pathway in the infected cells from which the E protein was obtained.