Identification and Analysis of a Novel Heparin-Binding Glycoprotein Encoded by Human Herpesvirus 7

Abstract

Human herpesvirus 6 (HHV-6) and HHV-7 are closely related betaherpesviruses that encode a number of genes with no known counterparts in other herpesviruses. The product of one such gene is the HHV-6 glycoprotein gp82-105, which is a major virion component and a target for neutralizing antibodies. A 1.7-kb cDNA clone from HHV-7 was identified which contains a large open reading frame capable of encoding a predicted primary translational product of 468 amino acids (54 kDa) with 13 cysteine residues and 9 potential N-linked glycosylation sites. This putative protein, which we have termed gp65, was homologous to HHV-6 gp105 (30% identity) and contained a single potential membrane-spanning domain located near its amino terminus. Comparison of the cDNA sequence with that of the viral genome revealed that the gene encoding gp65 contains eight exons, spanning almost 6 kb of the viral genome at the right (3) end of the HHV-7 genome. Northern (RNA) blot analysis with poly(A)؉ RNA from HHV-7-infected cells revealed that the cDNA insert hybridized to a single major RNA species of 1.7 kb. Antiserum raised against a purified, recombinant form of gp65 recognized a protein of roughly 65 kDa in sucrose density gradient-purified HHV-7 preparations; treatment with PNGase F reduced this glycoprotein to a putative precursor of approximately 50 kDa. Gp65-specific antiserum also neutralized the infectivity of HHV-7, while matched preimmune serum did not do so. Finally, analysis of the biochemical properties of recombinant gp65 revealed a specific interaction with heparin and heparan sulfate proteoglycans and not with closely related molecules such as N-acetylheparin and de-N-sulfated heparin. At least two domains of the protein were found to contribute to heparin binding. Taken together, these findings suggest that HHV-7 gp65 may contribute to viral attachment to cell surface proteoglycans.

The Human Herpesvirus 6 U100 Gene Product Is the Third Component of the gH-gL Glycoprotein Complex on the Viral Envelope

“…In that study, gp65 was detected in HHV-7 virions and interacted with heparin and heparan sulfate proteoglycans, and gp65-specific antiserum neutralized the infectivity of virus inocula (33). These findings suggested that HHV-7 gp65 may contribute to the attachment of the virus to cell surface proteoglycans (33).…”

“…Interestingly, gQ positional homologs have also been reported in human HHV-7, as HHV-7 gp65 (33). In that study, gp65 was detected in HHV-7 virions and interacted with heparin and heparan sulfate proteoglycans, and gp65-specific antiserum neutralized the infectivity of virus inocula (33).…”

“…The U100 gene open reading frame is predicted to encode a 650-amino-acid protein that has a potential signal peptide and no other hydrophobic sequence long enough to be membrane spanning and includes 11 potential N-linked glycosylation sites (29). The gene has an intron-exon structure, resulting in a highly spliced mRNA transcript, and is unique to HHV-6 and HHV-7 (29,33).…”

Herpesviruses and heparan sulfate: an intimate relationship in aid of viral entry

“…The It has been shown, however, that two HHV-7 glycoproteins, gB and a novel glycoprotein called gp65, can bind to heparin and heparan sulfate (22,23). By analogy with other herpesviruses, it seems likely that binding of these glycoproteins to heparan sulfate has a role in the binding of virus to cells.…”

Adaptation of Tick-Borne Encephalitis Virus to BHK-21 Cells Results in the Formation of Multiple Heparan Sulfate Binding Sites in the Envelope Protein and Attenuation In Vivo

“…Although the overall picture is still far from being complete, it has become clear during the past few years that viruses from many different families interact with GAGs, in most cases heparan sulfate (HS) (7,8,11,12,14,15,18,20,34,35,38,40,50,59,61,62,63,67,70), and it has been proposed that the affinity of the viral surface for HS may be an important determinant of tissue tropism and pathogenicity (5,9,17,30,48,65). In most cases the affinity of the virus for HS seems to be relatively low and may serve the purpose of concentrating the virus on the cell surface to facilitate subsequent binding to one or more high-affinity receptors (6,21,33,53,58).…”