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

Abstract

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.

Proteomics computational analyses suggest that baculovirus GP64 superfamily proteins are class III penetrenes

“…The leash sequence interacts with the external groove of the N-helix trimer. For other class I penetrenes the rearrange brings together the N-and C-helices into a six-helix bundle [46]. The F protein of isaviruses appears to utilize a leash-in-the groove mechanism of membrane fusion.…”

A membrane-associated movement protein of Pelargonium flower break virus shows RNA-binding activity and contains a biologically relevant leucine zipper-like motif

“…Whether this factor and/or different ones are recruited by p12 for directing viral transport remains to be seen. It is also worth mentioning that leucine zippers have been implicated in some instances in regulation of post-translational modification(s) rather than in promotion of protein-protein interactions (Long et al, 2008;Pagano et al, 2009). Such type of modifications might play an important role in MP activity (Kawakami et al, 2003).…”

Cell-Mediated Immunity in Elite Controllers Naturally Controlling HIV Viral Load

“…In particular, KIR3DL1 and KIR3DS1 have been associated with delayed progression to AIDS when interacting with HLA-B alleles. Thus, NK-mediated control of HIV replication has been also in cohorts of HIV+ individuals with spontaneous control of viral load (Martin et al, 2002, 2007; Lopez-Vazquez et al, 2005; Yawata et al, 2006; Alter et al, 2007; Long et al, 2008; Kamya et al, 2011a). Of note is that HIV controllers expressing HLA-Bw4*80I on target cells and KIR3DL1 on NK cells sustain a target cell-induced NK cytotoxicity stronger that that measured for CD8+ T cells from the same individuals (Tomescu et al, 2012).…”