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Journal of Virology, March 2008, p. 2437-2447, Vol. 82, No. 5
0022-538X/08/$08.00+0     doi:10.1128/JVI.01885-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Conserved Leucines in N-Terminal Heptad Repeat HR1 of Envelope Fusion Protein F of Group II Nucleopolyhedroviruses Are Important for Correct Processing and Essential for Fusogenicity{triangledown}

Gang Long ,1,2,{dagger},{ddagger} Xiaoyu Pan,1,{dagger} and Just M. Vlak2*

State Key Laboratory of Virology, Key Laboratory of Molecular Virology and Joint Laboratory of Invertebrate Virology, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan 43007, People's Republic of China,1 Laboratory of Virology, Wageningen University, Binnenhaven 11, 6709 PD Wageningen, The Netherlands2

Received 29 August 2007/ Accepted 12 December 2007

The heptad repeat (HR), a conserved structural motif of class I viral fusion proteins, is responsible for the formation of a six-helix bundle structure during the envelope fusion process. The insect baculovirus F protein is a newly found budded virus envelope fusion protein which possesses common features to class I fusion proteins, such as proteolytic cleavage and the presence of an N-terminal open fusion peptide and multiple HR domains on the transmembrane subunit F1. Similar to many vertebrate viral fusion proteins, a conserved leucine zipper motif is predicted in this HR region proximal to the fusion peptide in baculovirus F proteins. To facilitate our understanding of the functional role of this leucine zipper-like HR1 domain in baculovirus F protein synthesis, processing, and viral infectivity, key leucine residues (Leu209, Leu216, and Leu223) were replaced by alanine (A) or arginine (R), respectively. By using Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV) as a pseudotype expression system, we demonstrated that all mutant F proteins incorporated into budded virus, indicating that leucine substitutions did not affect intercellular trafficking of F. Furin-like protease cleavage was not affected by any of the leucine substitutions; however, the disulfide bridging and N-linked glycosylation patterns were partly altered. Single substitutions in HR1 showed that the three leucine residues were critical for F fusogenicity and the rescue of AcMNPV infectivity. Our results support the view that the leucine zipper-like HR1 domain is important to safeguard the proper folding, glycosylation, and fusogenicity of baculovirus F proteins.

* Corresponding author. Mailing address: Laboratory of Virology, Wageningen University, Binnenhaven 11, 6709 PD Wageningen, The Netherlands. Phone: 31-317-483090. Fax: 31-317-484820. E-mail: just.vlak{at}wur.nl

{triangledown} Published ahead of print on 19 December 2007.

{dagger} G.L. and X.P. contributed equally to this work.

{ddagger} Present address: Department of Molecular Virology, University of Heidelberg, D-69120 Heidelberg, Germany.

Journal of Virology, March 2008, p. 2437-2447, Vol. 82, No. 5
0022-538X/08/$08.00+0     doi:10.1128/JVI.01885-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Yu, I.-L., Bray, D., Lin, Y.-C., Lung, O. (2009). Autographa californica multiple nucleopolyhedrovirus ORF 23 null mutant produces occlusion-derived virions with fewer nucleocapsids. J. Gen. Virol. 90: 1499-1504 [Abstract] [Full Text]  


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