Lipid-anchored influenza hemagglutinin promotes hemifusion, not complete fusion

• Published in: Cell Vol. 76; no. 2; pp. 383 - 391
• Main Authors: Kemble, George W., Danieli, Tsafi, White, Judith M.
• Format: Journal Article
• Language: English
• Published: Cambridge, MA Elsevier Inc 28.01.1994; Cell Press
• Subjects: Base Sequence; Biological and medical sciences; Cell membranes. Ionic channels. Membrane pores; Cell structures and functions; DNA Primers - chemistry; Fundamental and applied biological sciences. Psychology; Glycosylphosphatidylinositols; Hemagglutinins, Viral - chemistry; In Vitro Techniques; influenza virus; Membrane Fusion; Membrane Lipids - chemistry; Molecular and cellular biology; Molecular Sequence Data; Orthomyxoviridae; Reaction intermediate; Membrane fusion; Hemagglutinin; Conformational dynamics; Monkey; Orthomyxoviridae; Glycoproteins; Influenzavirus; Mechanism; Kidney; Virus; Vertebrata; Mammalia; Glycophospholipid; Primates; Molecular accessibility
• ISSN: 0092-8674; 1097-4172
• DOI: 10.1016/0092-8674(94)90344-1

It has been proposed that membrane fusion events such as virus-cell fusion proceed through a hemifusion intermediate, a state where lipids but not contents of the fusing compartments mix. We engineered the influenza hemagglutinin (HA) such that it would be anchored in membranes via a glycosylphosphatidylinositol (GPI) tail. GPI-anchored HA forms a trimer that can bind red blood cells (RBCs) and change conformation under fusion-inducing conditions. Using RBCs labeled with fluorescent lipid or fluorescent soluble content probes, we found that GPI-anchored HA mediated lipid mixing with similar time course and efficiency as wt-HA, yet did not mediate transfer of soluble contents. Hence, GPI-anchored HA appears to initiate, but not complete, a fusion reaction. We interpret our results as evidence for uncoupling a physiological fusion reaction, for trapping a hemifusion intermediate, and for assigning a role to a transmembrane domain in a fusion event.