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.
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 F(1). 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.
Long
Gang
G
Laboratory of Virology, Wageningen University, Binnenhaven 11, 6709 PD Wageningen, The Netherlands.
Pan
Xiaoyu
X
Vlak
Just M
JM
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D017124:Conserved Sequence; D017931:DNA Primers; D006031:Glycosylation; D007930:Leucine / Q000502:physiology*; D008561:Membrane Fusion / Q000502:physiology*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D017924:Nucleopolyhedroviruses / Q000502:physiology*; D017510:Protein Folding; D017386:Sequence Homology, Amino Acid; D018411:Spodoptera; D014759:Viral Envelope Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*
D017931:DNA Primers; D014759:Viral Envelope Proteins; D007930:Leucine