Murine Anti-vaccinia Virus D8 Antibodies Target Different Epitopes and Differ in Their Ability to Block D8 Binding to CS-E

Authors:
Open Access
Publisher website
Google Scholar
Abstract
The IMV envelope protein D8 is an adhesion molecule and a major immunodominant antigen of vaccinia virus (VACV). Here we identified the optimal D8 ligand to be chondroitin sulfate E (CS-E). CS-E is characterized by a disaccharide moiety with two sulfated hydroxyl groups at positions 4′ and 6′ of GalNAc. To study the role of antibodies in preventing D8 adhesion to CS-E, we have used a panel of murine monoclonal antibodies, and tested their ability to compete with CS-E for D8 binding. Among four antibody specificity groups, MAbs of one group (group IV) fully abrogated CS-E binding, while MAbs of a second group (group III) displayed widely varying levels of CS-E blocking. Using EM, we identified the binding site for each antibody specificity group on D8. Recombinant D8 forms a hexameric arrangement, mediated by self-association of a small C-terminal domain of D8. We propose a model in which D8 oligomerization on the IMV would allow VACV to adhere to heterogeneous population of CS, including CS-C and potentially CS-A, while overall increasing binding efficiency to CS-E. Vaccinia virus (VACV) is an orthopox virus and considered the gold standard of vaccines as it was used to eradicate smallpox from the human population. Inoculation with VACV leads to a strong B cell immune response and the production of potent antibodies that simultaneously target several envelope proteins of the virus. Among those viral proteins, D8 is an adhesion molecule that binds chondroitin sulfate, a glycosaminoglycan, on the host cell surface. Here, we identified chondroitin sulfate E (CS-E), as the preferred ligand for D8 and assessed the role of a panel of anti-D8 antibodies in preventing D8 binding to CS-E. We further mapped the binding site of each antibody on the D8 surface to reveal the targeted epitopes. Finally, using several truncated D8 constructs, we identified that the C-terminal domain of D8 that is not involved in CS-E binding is in fact involved in oligomerization of native D8 in vitro and likely, also on the virion, as a means of increasing binding affinity to increase viral adhesion to CS on the host cell.

This publication has 39 references indexed in Scilit: