This Article Full Text Full Text (PDF) All Versions of this Article: biophysj.104.047696v1 87/5/3291    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Markosyan, R. M. Articles by Melikyan, G. B. Search for Related Content PubMed PubMed Citation Articles by Markosyan, R. M. Articles by Melikyan, G. B.

A Study of Low pH-Induced Refolding of Env of Avian Sarcoma and Leukosis Virus into a Six-Helix Bundle

R. M. Markosyan ^*, P. Bates , F. S. Cohen ^* and G. B. Melikyan ^*

^* Department of Molecular Biophysics and Physiology, Rush University Medical Center, Chicago, Illinois; and Department of Microbiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania

Correspondence: Address reprint requests to G. B. Melikyan, Dept. of Molecular Biophysics and Physiology, Rush Medical College, 1653 W. Congress Pkwy., Chicago, IL 60612. Tel.: 312-942-7011; Fax: 312-942-8711; E-mail: gmelikia{at}rush.edu.

The fusion protein of avian sarcoma and leukosis virus is likely to fold into a six-helix bundle as part of its final configuration. A peptide, R99, inhibits fusion, probably by binding into the grooves of the triple-stranded coiled coil that becomes the central core of the six-helix bundle. The stages at which the envelope protein (Env) of avian sarcoma and leukosis virus subgroup A folds into a bundle during low pH-induced fusion were determined. Effector cells expressing Env were bound to target cells expressing the cognate receptor Tva, and intermediates of fusion were created. R99 was added and the extent of fusion inhibition was used to distinguish between a prebundle state with exposed grooves and a state in which the grooves were no longer exposed. The native conformation of Env was not sensitive to R99. But adding a soluble form of Tva to effector cells conferred sensitivity. Acidic pH applied at low temperature created an intermediate state of local hemifusion. Surprisingly, R99 caused these locally hemifused membranes to separate. This indicates that the grooves of Env were still exposed, that prebundle configurations of Env stabilized hemifused states, and that binding of R99 altered the conformation of Env. In the presence of an inhibitory lipid that blocks fusion before hemifusion, applying low pH at 37°C created an intermediate in which R99 was without effect. This suggests that the six-helix bundle can form before hemifusion and that subsequent conformational changes, such as formation of the trimeric hairpin, are responsible for pore formation and/or growth.

This article has been cited by other articles:

				M. A. Zhukovsky, E. Leikina, I. Markovic, A. L. Bailey, and L. V. Chernomordik Heterogeneity of Early Intermediates in Cell-Liposome Fusion Mediated by Influenza Hemagglutinin Biophys. J., November 1, 2006; 91(9): 3349 - 3358. [Abstract] [Full Text] [PDF]

				J. A. Corcoran, J. Salsman, R. de Antueno, A. Touhami, M. H. Jericho, E. K. Clancy, and R. Duncan The p14 Fusion-associated Small Transmembrane (FAST) Protein Effects Membrane Fusion from a Subset of Membrane Microdomains J. Biol. Chem., October 20, 2006; 281(42): 31778 - 31789. [Abstract] [Full Text] [PDF]

				M. Wallin, M. Ekstrom, and H. Garoff Receptor-Triggered but Alkylation-Arrested Env of Murine Leukemia Virus Reveals the Transmembrane Subunit in a Prehairpin Conformation J. Virol., October 1, 2006; 80(19): 9921 - 9925. [Abstract] [Full Text] [PDF]

				M. Wallin, R. Loving, M. Ekstrom, K. Li, and H. Garoff Kinetic Analyses of the Surface-Transmembrane Disulfide Bond Isomerization-Controlled Fusion Activation Pathway in Moloney Murine Leukemia Virus J. Virol., November 15, 2005; 79(22): 13856 - 13864. [Abstract] [Full Text] [PDF]