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Journal of Virology, May 2005, p. 6216-6226, Vol. 79, No. 10
0022-538X/05/$08.00+0     doi:10.1128/JVI.79.10.6216-6226.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Unusual Topological Arrangement of Structural Motifs in the Baboon Reovirus Fusion-Associated Small Transmembrane Protein

Sandra Dawe,{dagger} Jennifer A. Corcoran,{ddagger} Eileen K. Clancy, Jayme Salsman, and Roy Duncan*

Department of Microbiology and Immunology, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4H7

Received 2 November 2004/ Accepted 6 January 2005

Select members of the Reoviridae are the only nonenveloped viruses known to induce syncytium formation. The fusogenic orthoreoviruses accomplish cell-cell fusion through a distinct class of membrane fusion-inducing proteins referred to as the fusion-associated small transmembrane (FAST) proteins. The p15 membrane fusion protein of baboon reovirus is unique among the FAST proteins in that it contains two hydrophobic regions (H1 and H2) recognized as potential transmembrane (TM) domains, suggesting a polytopic topology. However, detailed topological analysis of p15 indicated only the H1 domain is membrane spanning. In the absence of an N-terminal signal peptide, the H1 TM domain serves as a reverse signal-anchor to direct p15 membrane insertion and a bitopic Nexoplasmic/Ccytoplasmic topology. This topology results in the translocation of the smallest ectodomain (~20 residues) of any known viral fusion protein, with the majority of p15 positioned on the cytosolic side of the membrane. Mutagenic analysis indicated the unusual presence of an N-terminal myristic acid on the small p15 ectodomain is essential to the fusion process. Furthermore, the only other hydrophobic region (H2) present in p15, aside from the TM domain, is located within the endodomain. Consequently, the p15 ectodomain is devoid of a fusion peptide motif, a hallmark feature of membrane fusion proteins. The exceedingly small, myristoylated ectodomain and the unusual topological distribution of structural motifs in this nonenveloped virus membrane fusion protein necessitate alternate models of protein-mediated membrane fusion.

* Corresponding author. Mailing address: Department of Microbiology and Immunology, Faculty of Medicine, Dalhousie University, Halifax, Nova Scotia, Canada B3H 1X5. Phone: (902) 494-6770. Fax: (902) 494-5125. E-mail: roy.duncan{at}dal.ca.

{dagger} Present address: McArdle Laboratory for Cancer Research, University of Wisconsin, Madison, WI 53706.

{ddagger} Present address: Department of Medical Microbiology and Immunology, Heritage Medical Research Building, University of Alberta, Edmonton, Alberta, Canada T6G 2S2.

Journal of Virology, May 2005, p. 6216-6226, Vol. 79, No. 10
0022-538X/05/$08.00+0     doi:10.1128/JVI.79.10.6216-6226.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

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