Sequential Conformational Changes in the Morbillivirus Attachment Protein Initiate the Membrane Fusion Process

PLoS Pathogens

Lisa Alves¹  Nadine Ader-Ebert¹  Claes Örvell¹  Michael Herren¹  Andreas Zurbriggen¹  Philippe Plattet¹  Richard K. Plemper²  Fanny Bringolf²  Mislay Avila²  Johannes P. Langedijk²  Mojtaba Khosravi² 

[1] Division of Neurological Sciences, Department of Clinical Research and Veterinary Public Health (DCR-VPH), Vetsuisse Faculty, University of Bern, Bern, Switzerland;Graduate School for Cellular and Biomedical Sciences, University of Bern, Bern, Switzerland

关键词: Membrane fusion;    Cell fusion;    Vero cells;    Flow cytometry;    Cell binding;    Cell membranes;    Membrane proteins;    Viral entry;   

DOI  :  10.1371/journal.ppat.1004880

学科分类：生物科学（综合）

来源: Public Library of Science

【 摘 要 】

Despite large vaccination campaigns, measles virus (MeV) and canine distemper virus (CDV) cause major morbidity and mortality in humans and animals, respectively. The MeV and CDV cell entry system relies on two interacting envelope glycoproteins: the attachment protein (H), consisting of stalk and head domains, co-operates with the fusion protein (F) to mediate membrane fusion. However, how receptor-binding by the H-protein leads to F-triggering is not fully understood. Here, we report that an anti-CDV-H monoclonal antibody (mAb-1347), which targets the linear H-stalk segment 126-133, potently inhibits membrane fusion without interfering with H receptor-binding or F-interaction. Rather, mAb-1347 blocked the F-triggering function of H-proteins regardless of the presence or absence of the head domains. Remarkably, mAb-1347 binding to headless CDV H, as well as standard and engineered bioactive stalk-elongated CDV H-constructs treated with cells expressing the SLAM receptor, was enhanced. Despite proper cell surface expression, fusion promotion by most H-stalk mutants harboring alanine substitutions in the 126-138 “spacer” section was substantially impaired, consistent with deficient receptor-induced mAb-1347 binding enhancement. However, a previously reported F-triggering defective H-I98A variant still exhibited the receptor-induced “head-stalk” rearrangement. Collectively, our data spotlight a distinct mechanism for morbillivirus membrane fusion activation: prior to receptor contact, at least one of the morbillivirus H-head domains interacts with the membrane-distal “spacer” domain in the H-stalk, leaving the F-binding site located further membrane-proximal in the stalk fully accessible. This “head-to-spacer” interaction conformationally stabilizes H in an auto-repressed state, which enables intracellular H-stalk/F engagement while preventing the inherent H-stalk’s bioactivity that may prematurely activate F. Receptor-contact disrupts the “head-to-spacer” interaction, which subsequently “unlocks” the stalk, allowing it to rearrange and trigger F. Overall, our study reveals essential mechanistic requirements governing the activation of the morbillivirus membrane fusion cascade and spotlights the H-stalk “spacer” microdomain as a possible drug target for antiviral therapy.

【 授权许可】

CC BY