Protein Science, Vol 7, Issue 11 2359-2373, Copyright © 1998 by Cold Spring Harbor Laboratory Press

ARTICLE

pH-Induced conformational changes of membrane-bound influenza hemagglutinin and its effect on target lipid bilayers

C. GRAY and L. K. TAMM
Department of Molecular Physiology and Biological Physics, University of Virginia Health Sciences Center, P.O. Box 10011, Charlottesville, Virginia 22906-0011

Influenza virus hemagglutinin (HA) has served as a paradigm for both pH-dependent and -independent viral membrane fusion. Although large conformational changes were observed by X-ray crystallography when soluble fragments of HA were subjected to fusion-pH conditions, it is not clear whether the same changes occur in membrane-bound HA, what the spatial relationship is between the conformationally changed HA and the target and viral membranes, and in what way HA perturbs the target membrane at low pH. We have taken a spectroscopic approach using an array of recently developed FTIR techniques to address these questions. Difference attenuated total reflection FTIR spectroscopy was employed to reveal reversible and irreversible components of the pH-induced conformational change of the membrane-bound bromelain fragment of HA, BHA. Additional proteolytic fragments of BHA were produced which permitted a tentative assignment of the observed changes to the HA(1) and HA(2) subunits, respectively. The membrane-bound HA(1) subunit undergoes a reversible conformational change, which most likely involves the loss of a small proportion of {beta}-sheet at low pH. BHA was found to undergo a partially reversible tilting motion relative to the target membrane upon exposure to pH 5, indicating a previously undescribed hinge near the anchoring point to the target membrane. Time-resolved amide H/D exchange experiments revealed a more dynamic (tertiary) structure of membrane-bound BHA and its HA(2), but not its HA(1), subunit. Finally BHA and, to a lesser degree, HA(1) perturbed the lipid bilayer of the target membrane at the interface, as assessed by spectral changes of the lipid ester carbonyl groups. These results are discussed in the context of a complementary study of HA that was bound to viral membranes through its transmembrane peptide (Gray C, Tamm LK, 1997, Protein Sci 6:1993-2006). A distinctive role for the HA(1) subunit in the conformational change of HA becomes apparent from these combined studies.
CiteULike    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				Y. Li, X. Han, A. L. Lai, J. H. Bushweller, D. S. Cafiso, and L. K. Tamm Membrane Structures of the Hemifusion-Inducing Fusion Peptide Mutant G1S and the Fusion-Blocking Mutant G1V of Influenza Virus Hemagglutinin Suggest a Mechanism for Pore Opening in Membrane Fusion J. Virol., September 15, 2005; 79(18): 12065 - 12076. [Abstract] [Full Text] [PDF]

				M. Shmulevitz, R. F. Epand, R. M. Epand, and R. Duncan Structural and Functional Properties of an Unusual Internal Fusion Peptide in a Nonenveloped Virus Membrane Fusion Protein J. Virol., March 15, 2004; 78(6): 2808 - 2818. [Abstract] [Full Text] [PDF]

				M. S. Celej, G. G. Montich, and G. D. Fidelio Protein stability induced by ligand binding correlates with changes in protein flexibility Protein Sci., July 1, 2003; 12(7): 1496 - 1506. [Abstract] [Full Text] [PDF]

				B. D. Zelus, J. H. Schickli, D. M. Blau, S. R. Weiss, and K. V. Holmes Conformational Changes in the Spike Glycoprotein of Murine Coronavirus Are Induced at 37{degrees}C either by Soluble Murine CEACAM1 Receptors or by pH 8 J. Virol., December 20, 2002; 77(2): 830 - 840. [Abstract] [Full Text] [PDF]

				E. Leikina and L. V. Chernomordik Reversible Merger of Membranes at the Early Stage of Influenza Hemagglutinin-mediated Fusion Mol. Biol. Cell, July 1, 2000; 11(7): 2359 - 2371. [Abstract] [Full Text]

				P. Bonnafous and T. Stegmann Membrane Perturbation and Fusion Pore Formation in Influenza Hemagglutinin-mediated Membrane Fusion. A NEW MODEL FOR FUSION J. Biol. Chem., February 25, 2000; 275(9): 6160 - 6166. [Abstract] [Full Text] [PDF]

				S. E. Delos, J. M. Gilbert, and J. M. White The Central Proline of an Internal Viral Fusion Peptide Serves Two Important Roles J. Virol., February 15, 2000; 74(4): 1686 - 1693. [Abstract] [Full Text]

				H. Qiao, R. T. Armstrong, G. B. Melikyan, F. S. Cohen, and J. M. White A Specific Point Mutant at Position 1 of the Influenza Hemagglutinin Fusion Peptide Displays a Hemifusion Phenotype Mol. Biol. Cell, August 1, 1999; 10(8): 2759 - 2769. [Abstract] [Full Text]