O-glycoprotein biosynthesis: site localization by Edman degradation and site prediction based on random peptide substrates

Sialic Acids on Varicella-Zoster Virus Glycoprotein B Are Required for Cell-Cell Fusion

Varicella-zoster virus (VZV) is a member of the human Herpesvirus family that causes varicella (chicken pox) and zoster (shingles). VZV latently infects sensory ganglia and is also responsible for encephalomyelitis. Myelin-associated glycoprotein (MAG), a member of the sialic acid (SA)-binding immunoglobulin-like lectin family, is mainly expressed in neural tissues. VZV glycoprotein B (gB) associates with MAG and mediates membrane fusion during VZV entry into host cells. The SA requirements of MAG when associating with its ligands vary depending on the specific ligand, but it is unclear whether the SAs on gB are involved in the association with MAG. In this study, we found that SAs on gB are essential for the association with MAG as well as for membrane fusion during VZV infection. MAG with a point mutation in the SA-binding site did not bind to gB and did not mediate cell-cell fusion or VZV entry. Cell-cell fusion and VZV entry mediated by the gB-MAG interaction were blocked by sialidase treatment. N-glycosylation or O-glycosylation inhibitors also inhibited the fusion and entry mediated by gB-MAG interaction. Furthermore, gB with mutations in N-glycosylation sites, i.e. asparagine residues 557 and 686, did not associate with MAG, and the cell-cell fusion efficiency was low. Fusion between the viral envelope and cellular membrane is essential for host cell entry by herpesviruses. Therefore, these results suggest that SAs on gB play important roles in MAG-mediated VZV infection.

A new role for mucins in immunity: insights from gastrointestinal nematode infection

The body's mucosal surfaces are protected from pathogens and physical and chemical attack by the gel-like extracellular matrix, mucus. The framework of this barrier is provided by polymeric, gel-forming mucins. These enormous O-linked glycoproteins are synthesised, stored and secreted by goblet cells that are also the source of other protective factors. Immune regulation of goblet cells during the course of infection impacts on mucin production and properties and ultimately upon barrier function. The barrier function of mucins in protection of the host is well accepted as an important aspect of innate defence. However, it is becoming increasingly clear that mucins have a much more direct role in combating pathogens and parasites and are an important part of the coordinated immune response to infection. Of particular relevance to this review is the finding that mucins are essential anti-parasitic effector molecules. The current understanding of the roles of these multifunctional glycoproteins, and other goblet cell products, in mucosal defence against intestinal dwelling nematodes is discussed.