Paramyxovirus entry into cells requires the fusion protein (F) and a receptor binding protein (HN, H or G). The multifunctional hemagglutinin-neuraminidase (HN) protein of some paramyxoviruses, besides functioning as the receptor (sialic acid) binding protein (hemagglutinin activity) and the receptor-destroying protein (neuraminidase activity), enhances fusion protein (F) activity, presumably by lowering the activation energy required for F to mediate fusion of viral and cellular membranes. Before or upon receptor binding by the HN globular head, F is believed to interact with the HN stalk. Unfortunately until recently none of the receptor binding protein crystal structures have shown electron density for the stalk domain. Parainfluenza virus 5 (PIV5) HN exists as a non-covalent dimer-of-dimers on the surface of cells, linked by a single disulfide bond in the stalk. Here we present the crystal structure of the PIV5-HN stalk domain at a resolution of 2.65 A revealing a four-helix bundle (4HB) with an upper (N-terminal) straight region and a lower (C-terminal) supercoiled part. The hydrophobic core residues are a mix of an 11-mer repeat and a 3-4 heptad repeat. To functionally characterize the role of the HN stalk in F-interactions and fusion, we designed mutants along the PIV5-HN stalk that are N-glycosylated to physically disrupt F-HN interactions. By extensive study of receptor binding, neuraminidase activity, oligomerization and fusion promoting functions of the mutant proteins we found a correlation between the position of the N-glycosylation mutants on the stalk structure and their neuraminidase activities as well as their abilities to promote fusion.
Structure and mutagenesis of the parainfluenza virus 5 hemagglutinin-neuraminidase stalk domain reveals a four-helix bundle and the role of the stalk in fusion promotion.,Bose S, Welch BD, Kors CA, Yuan P, Jardetzky TS, Lamb RA J Virol. 2011 Oct 12. PMID:21994464
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↑ Bose S, Welch BD, Kors CA, Yuan P, Jardetzky TS, Lamb RA. Structure and mutagenesis of the parainfluenza virus 5 hemagglutinin-neuraminidase stalk domain reveals a four-helix bundle and the role of the stalk in fusion promotion. J Virol. 2011 Oct 12. PMID:21994464 doi:10.1128/JVI.06350-11