Fusogenic Domains in Herpes Simplex Virus Type 1 Glycoprotein H

Abstract

Infection of eukaryotic cells by enveloped viruses requires fusion between the viral envelope and the cellular plasma or endosomal membrane. The actual merging of the two membranes is mediated by viral envelope glycoproteins, which generally contain a highly hydrophobic region termed the fusion peptide. The entry of herpesviruses is mediated by three conserved proteins: glycoproteins B, H (gH), and L. However, how fusion is executed remains unknown. Herpes simplex virus type 1 gH exhibits features typical of viral fusion glycoproteins, and its ectodomain seems to contain a putative internal fusion peptide. Here, we have identified additional internal segments able to interact with membranes and to induce membrane fusion of large unilamellar vesicles. We have applied the hydrophobicity-atinterface scale proposed by Wimley and White (Wimley, W. C., and White, S. H. (1996) Nat. Struct. Biol. 3, 842-848) to identify six hydrophobic stretches within gH with a tendency to partition into the membrane interface, and four of them were able to induce membrane fusion. Experiments in which equimolar mixtures of gH peptides were used indicated that different fusogenic regions may act in a synergistic way. The functional and structural characterization of these segments suggests that herpes simplex virus type 1 gH possesses several fusogenic internal peptides that could participate in the actual fusion event.

Analysis of a Membrane Interacting Region of Herpes Simplex Virus Type 1 Glycoprotein H

“…Peptide Synthesis-Peptides were synthesized using standard solid-phase 9-fluorenylmethoxycarbonyl (Fmoc) method as reported previously (20). All purified peptides were obtained with good yields (30 -40%).…”

“…However, their spectra were consistent with the peptides becoming more structured in low polarity solvent as increasing amounts of TFE induced stabilization of ␣-helical structures. We previously reported (20) that the peptide gH-(626 -644) changed from a random coil to an ␣-helix upon membrane binding, and in fact the spectrum in SDS was typical of a helix. We now compared the spectrum of the native sequence in SDS with those of the mutant peptides.…”

“…These data allowed the identification of a putative fusion peptide in gB and suggested the identification of a third class of fusion proteins. Although no structural data for gH/gL from HSV-1 (or any of its homologues in other herpesviruses) are available, gH has also been considered as a likely fusion effector (20,21).…”

“…For example, certain mutations in the transmembrane region and cytoplasmic tail affect fusion (27,28), as do mutations in the region preceding the transmembrane (24). Furthermore, peptides matching a number of regions of the gH ectodomain have been shown to interact with membranes and have been proposed to play a role in the fusion process (20,21).…”

Herpes Simplex Virus gD Forms Distinct Complexes with Fusion Executors gB and gH/gL in Part through the C-terminal Profusion Domain

“…Thus, gH carries elements typical of fusion glycoproteins, i.e. hydrophobic regions able to interact with target cells or artificial membranes and two heptad repeats potentially able to form a coiled coil (13)(14)(15)(16)(17)(18). Peptides mimicking the hydrophobic regions of gH promote fusion of artificial membranes (19,20).…”