A Multipotential β -1,6-N-acetylglucosaminyltransferase Is Encoded by Bovine Herpesvirus Type 4

The β -1,6-N-acetylglucosaminyltransferase (β 1,6GnT) gene family encodes enzymes playing crucial roles in glycan synthesis. Important changes in β 1,6GnT expression are observed during development, oncogenesis, and immunodeficiency. The most characterized β 1,6GnTs in this gene family are the human (h) C2GnT-L and h-IGnT, which have core 2[Galβ 1→ 3(GlcNAcβ 1→ 6)GalNAc] and I branching [GlcNAcβ 1→ 3(GlcNAcβ 1→ 6)Gal] activities, respectively. Recently, h-C2GnT-M was shown to be unique in forming core 2, core 4 [GlcNAcβ 1→ 3(GlcNAcβ 1→ 6)GalNAc], and I structures. To date, the β 1,6GnT gene family has been characterized only in mammals. Here, we describe that bovine herpesvirus type 4 (BHV-4) encodes a β 1,6GnT expressed during viral replication and exhibiting all of the core 2, core 4, and I branching activities. Sequencing of the BHV-4 genome revealed an ORF, hereafter called BORFF3-4, encoding a protein (pBORFF3-4) exhibiting 81.1%, 50.7%, and 36.6% amino acid identity with h-C2GnT-M, h-C2GnT-L, and h-IGnT, respectively. Reverse transcriptase-PCR analysis revealed that BORFF3-4 is expressed during BHV-4 replication. Expression of BORFF3-4 in Chinese hamster ovary cells directed the expression of core 2 branched oligosaccharides and I antigenic structures on the cell surface. Moreover, a soluble form of pBORFF3-4 had core 4 branching activity in addition to core 2 and I branching activities. Finally, infection of a C2GnT-negative cell line with BHV-4 induced expression of core 2 branched oligosaccharides. This study extends the β 1,6GnT gene family to a viral gene and provides a model to study the biological functions of a β 1,6GnT in the context of viral infection.