Fig. 1.  O-glycosylation of herpesvirus conserved fusion machinery. (A), Crystal structure representation of HSV-1 gB monomer. From “Heldwein EE Lou H Bender FC Cohen GH Eisenberg RJ Harrison S 2006. Crystal structure of glycoprotein B from herpes simplex virus 1. Science, 313:217–220”. Reprinted with permission from AAAS. Blue boxes mark the parts of the molecule where O-glycans are consistently found between at least two investigated herpesviruses. Modified with permission from the authors. (B), (D) and (F), Conservation of O-linked glycosylation sites on homologous envelope glycoproteins of human herpesviruses (from Bagdonaite et al., 2016). Reprinted with permission. © 2008 The American Society for Biochemistry and Molecular Biology. All rights reserved. Clustal Omega server was used to align amino acid sequences of gB (B), gH (D) and gL (F) between HSV-1 (Bagdonaite et al. 2015), HSV-2 (Iversen et al. 2016), VZV (Bagdonaite et al. 2016), HCMV (Bagdonaite et al. 2016) and EBV (Bagdonaite et al. 2016). Protein backbones are depicted as broken black lines, where spaces represent gaps in the alignment. Individual alignments were drawn to scale (indicated below each graph). Sequence conservation is indicated above the aligned sequences for each set, and is represented by a greyscale barcode that maps to the clustal alignment score, as shown in the legend. In brief, for the clustal alignment score, an asterisk indicates positions with fully conserved residues, a colon indicates conservation of amino acids with strongly similar properties, whereas a period indicates conservation of amino acids with weakly similar properties. Predicted signal peptides and transmembrane regions are shaded in pink and blue, respectively. Unambiguous O-glycosylation sites are shown as yellow squares, whereas ambiguous sites are marked as yellow lines within the protein backbone, where the number below indicates the number of glycosites. An ambiguous O-glycosylation site from our previous publication (Bagdonaite et al. 2015, HSV-1 gB 109–123 (HexHexNAc)) was omitted from the graph, as we cannot exclude the possibility it could be part of an elongated structure on an adjacent site. Reference strain sequences were used for HSV-2, VZV and EBV due to incomplete or unavailable annotation of investigated strains. HSV-1—human herpes simplex virus type 1 (strain 17), HSV-2—human herpes simplex virus type 2 (strain HG52), VZV—varicella-zoster virus (strain Dumas), HCMV—human cytomegalovirus (strain Towne), EBV—Epstein-Barr virus (strain AG876). (C) and (E) Cartoon depiction of HSV-1 gB trimers (C) or gH–gL complexes and accessory proteins (E) of the five herpesviruses. O-glycosylation sites are shown as yellow squares. (B) and (C) Colored boxes mark association with herpesvirus gB domains as defined in (A).