The C Terminus of the B5 Receptor for Herpes Simplex Virus Contains a Functional Region Important for Infection

Abstract

. 79:7419-7430, 2005). Heptad repeats found in the B5 C terminus are predicted to form an ␣-helix for coiled coil structure. We used mutagenesis and synthetic peptides with wild-type and mutant sequences to examine the function of the heptad repeat motif in HSV binding and entry into porcine cells that express B5 and for infection of naturally susceptible human HEp-2 cells. B5 with point mutations predicted to disrupt the putative C-terminal coiled coil failed to mediate HSV binding and entry into porcine cells. Synthetic peptides that contain the single amino acid changes lose the blocking activity of HSV entry. We concluded that the C terminus of B5 contains a functional region that is important for the B5 receptor to mediate events in HSV entry. Structural evidence that this functional region forms coiled coil structures is under investigation. Blocking of HSV interaction with the C-terminal region of the B5 receptor is a new potential target site to intervene in the virus infection of human cells.Herpes simplex virus (HSV) is a prevalent human pathogen that establishes a lifelong infection in its human host. It replicates at the site of entry into the host, most typically to cause oral or genital lesions. Latency is established in neuronal cells from which it reactivates periodically to cause recurrent lesions. The immune system of a healthy person usually can limit lesions to a small localized area. However, HSV causes severe complications and morbidity for immunosuppressed, chronically ill, or bedridden individuals (20,23). Accumulating evidence suggests a possible role for HSV or other infectious agents in the development of neurodegenerative disease (11,12,39).A recently characterized human gene designated human fetal lung cDNA B5 (hfl-B5) (32a) is expressed in a wide range of tissues and encodes a 43-kDa gene product (B5) that mediates HSV entry. Its features differ from the known human receptor proteins for HSV that engage glycoprotein D (gD) (41). The viral ligand for B5 has not yet been determined. The hfl-B5 sequence contains heptad repeats strongly predicted to form coiled coil structure. Coiled coils are composed of leucine zipper motifs that form ␣-helices (16). Two or more ␣-helices supercoil around one another to associate in a parallel or antiparallel orientation. Mutagenesis of apolar residues that are positioned to form a hydrophobic core in the ␣-helix of the heptad repeat (25, 26) have been shown to alter ␣-helix conformation. Point mutations for influenza, human immunodeficiency virus (HIV) gp41 or other viral proteins alter ␣-helix formation and disrupt viral-induced membrane fusion (1,4,5,10,15,34,43). They have been identified as functional features in some cellular and viral fusion proteins (6, 40).Although the mechanisms by which viruses fuse membranes at entry or spread are not yet clear, heptad repeats are a functional part of fusion machinery in a growing number of viral fusion proteins (3,13,28,40). The first characterized of these are hemagglutinin (HA) of influenza virus (34) a...

A New Class of Receptor for Herpes Simplex Virus Has Heptad Repeat Motifs That Are Common to Membrane Fusion Proteins

“…Point mutations predicted to break the ␣-helix in the C terminus of B5 result in proteins that do not support HSV entry (24). This indicates an important function of the Cterminal region.…”

“…On the basis of analogies with viral entry or cell fusion proteins (5,13,16,17,28,31), we hypothesize that the predicted B5 C-terminal coiled coil may engage those found in an essential HSV glycoprotein or possibly in an as-yet-unknown accessory cellular protein. Computer-based analyses of HSV glycoprotein sequences show that only gH and gL contain heptad repeats with predicted high scoring ␣-helices (24). gH and gL are essential for HSV entry and cell fusion (2, 10, 29).…”

Peptide Antimicrobial Agents

“…Recently a new HSV entry receptor was described (196); it is effectively blocked by binding of an ␣-helical peptide in a coiled-coil formation (197). Whether this receptor is specific for HSV-1 or also allows HSV-2 entry is unknown; therefore, this cannot definitively explain differences in the antiviral effects of peptides on the two viruses.…”

Formation and Reversible Dissociation of Coiled Coil of Peptide to the C-Terminus of the HSV B5 Protein: A Time-Resolved Spectroscopic Analysis

“…Computational analysis showed that the C-terminus (amino acids 344-374) of B5 has a high probability of forming an a-helical coiled coil (7)(8)(9). This is particularly interesting, since computational modeling has also shown that it is highly possible that gH and gL form coiled coils (8)(9)(10).…”