Glycoprotein that probably modulates membrane fusion events during secondary envelopment of cytoplasmic capsids that bud into specific trans-Golgi network (TGN)-derived membranes. Also plays a role, together with gB, in virus-induced cell-to-cell fusion (syncytia formation). Seems to block fusion of virions with infected-cell membranes. Interacts (via UL20 interaction region) with protein UL20 (via N-terminus); this interaction probably plays a role in the coordinate transport of protein UL20 and gK to the trans-Golgi network (TGN), and is required for the cell surface expression of gK. During virion morphogenesis, this protein probably accumulates in the endosomes and trans-Golgi where secondary envelopment occurs. It is probably transported with UL20 to the cell surface from where it is endocytosed and directed to the trans-Golgi network (TGN). Cell surface expression of gK is required for virus-induced cell-to-cell fusion. Likely not present in extracellular virions. N-glycosylated. Belongs to the alphaherpesvirinae glycoprotein K family.