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Biochemistry. 2018 Aug 24. doi: 10.1021/acs.biochem.8b00764. [Epub ahead of print]
Stabilities of the Soluble Ectodomain and Fusion Peptide Hairpins of the Influenza Virus Hemagglutinin Subunit II Protein Are Positively-Correlated with Membrane Fusion.
Ranaweera A, Ratnayake PU, Weliky DP.
Abstract
Cellular entry of influenza virus is mediated by the viral protein hemagglutinin(HA), which forms an initial complex of three HA1 and three HA2 subunits. Each HA2 includes a fusion peptide(FP), soluble ectodomain(SE), and transmembrane domain. HA1 binds to cellular sialic acids, followed by virus endocytosis, pH reduction, dissociation of HA1, and HA2 structural rearrangement into a final trimer-of-SE hairpins. pH reduction also triggers HA2-mediated virus/endosome membrane fusion. SE hairpins have an interior parallel helical bundle and C-terminal strands in the grooves of the bundle exterior. FP's are separate helical hairpins. The present study compares WT-HA2 with G1E(FP) and I173E(SE strand) mutants. WT-HA2 induces vesicle fusion at pH 5.0, whereas fusion is greatly reduced for both mutants. Circular dichroism for HA2 and FHA2(FP+SE) constructs show dramatic losses in stability for the mutants, including a Tm reduced by 40 oC for I173E-FHA2. This evidences destabilization of SE hairpins via dissociation of strands from the helical bundle, which is also supported by larger monomer fractions for mutant vs. WT proteins. The G1E mutant may have disrupted FP hairpins, with consequent non-native FP binding to dissociated SE strands. It is commonly proposed that free energy released by the HA2 structural rearrangement catalyzes HA-mediated fusion. The present study supports an alternate mechanistic model in which fusion is preceded by FP insertion in the target membrane and formation of the final SE hairpin. Lower fusion by the mutants is due to loss of hairpin stability and consequent reduced membrane apposition of the virus and target membranes.
PMID: 30141905 DOI: 10.1021/acs.biochem.8b00764
Stabilities of the Soluble Ectodomain and Fusion Peptide Hairpins of the Influenza Virus Hemagglutinin Subunit II Protein Are Positively-Correlated with Membrane Fusion.
Ranaweera A, Ratnayake PU, Weliky DP.
Abstract
Cellular entry of influenza virus is mediated by the viral protein hemagglutinin(HA), which forms an initial complex of three HA1 and three HA2 subunits. Each HA2 includes a fusion peptide(FP), soluble ectodomain(SE), and transmembrane domain. HA1 binds to cellular sialic acids, followed by virus endocytosis, pH reduction, dissociation of HA1, and HA2 structural rearrangement into a final trimer-of-SE hairpins. pH reduction also triggers HA2-mediated virus/endosome membrane fusion. SE hairpins have an interior parallel helical bundle and C-terminal strands in the grooves of the bundle exterior. FP's are separate helical hairpins. The present study compares WT-HA2 with G1E(FP) and I173E(SE strand) mutants. WT-HA2 induces vesicle fusion at pH 5.0, whereas fusion is greatly reduced for both mutants. Circular dichroism for HA2 and FHA2(FP+SE) constructs show dramatic losses in stability for the mutants, including a Tm reduced by 40 oC for I173E-FHA2. This evidences destabilization of SE hairpins via dissociation of strands from the helical bundle, which is also supported by larger monomer fractions for mutant vs. WT proteins. The G1E mutant may have disrupted FP hairpins, with consequent non-native FP binding to dissociated SE strands. It is commonly proposed that free energy released by the HA2 structural rearrangement catalyzes HA-mediated fusion. The present study supports an alternate mechanistic model in which fusion is preceded by FP insertion in the target membrane and formation of the final SE hairpin. Lower fusion by the mutants is due to loss of hairpin stability and consequent reduced membrane apposition of the virus and target membranes.
PMID: 30141905 DOI: 10.1021/acs.biochem.8b00764