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Journal of Virology, May 2007, p. 4858-4865, Vol. 81, No. 9
0022-538X/07/$08.00+0     doi:10.1128/JVI.02755-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Mutational Evidence of Internal Fusion Loops in Herpes Simplex Virus Glycoprotein B

Brian P. Hannah,^1* Ekaterina E. Heldwein,^2, Florent C. Bender,¹ Gary H. Cohen,¹ and Roselyn J. Eisenberg³

Department of Microbiology, School of Dental Medicine,¹ Department of Pathology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104,³ Children's Hospital and Harvard Medical School, Boston, Massachusetts 02155²

Received 14 December 2006/ Accepted 9 February 2007

Herpes simplex virus type 1 (HSV-1) glycoprotein B (gB) is one of four glycoproteins necessary and sufficient for HSV cellular entry. Recently, the crystal structures of HSV-1 gB and vesicular stomatitis virus glycoprotein G were determined. Surprisingly, the two proteins share remarkable structural homology. Both proteins are homotrimeric and center about a long alpha-helix, features reminiscent of class I fusion proteins, such as influenza virus hemagglutinin or paramyxovirus F. However, these structures revealed that G has internal fusion loops, similar to the fusion loops of the class II fusion proteins, and that these loops are structurally conserved in gB. To examine whether these putative fusion loops are important for gB function, we mutated potential membrane-interacting (hydrophobic) residues to charged amino acids. Of most interest were mutant gB proteins that were expressed on the cell surface and were recognized by monoclonal antibodies against conformational epitopes but lacked the ability to function in cell-cell fusion assays. We find that three of the five hydrophobic amino acids targeted in these loops, tryptophan 174, tyrosine 179, and alanine 261, are integral in the function of gB. Our data suggest that they are part of an important functional domain. We hypothesize that two loops in domain 1 of HSV gB function as fusion loops. Our data are further evidence that gB is a viral fusogen and suggest clues as to how gB may function.

Published ahead of print on 21 February 2007.

Present address: Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, MA 02111.

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