N- and C-terminal external domains of human herpesvirus-6 glycoprotein H affect a fusion-associated conformation mediated by glycoprotein L binding the N terminus.

Abstract

Human herpesvirus-6 (HHV-6), like other betaherpesviruses, shows cell fusion with wild-type strains, and this cellular spread is mediated by the glycoprotein gH/gL complex. Anti-fusion monoclonal antibodies (MAbs) specific for HHV-6 glycoprotein gH inhibit infection and prevent cellular spread by syncytia formation. Reactivity of these MAbs with gH deletion mutants suggests a conserved C-terminal fusion-associated domain. A conserved motif here has an N-glycosylation site and characteristics of a beta turn. Motif deletion abrogated MAb recognition while coexpression with glycoprotein gL restored this conformational epitope, indicating the importance of folding and not glycosylation at this site. Our previous studies showed gL binding to gH at an Nterminal domain specific for betaherpesviruses. To further examine the function of this N-terminal domain, a betaherpesvirus-specific motif was deleted. This mutant gH still bound gL, and was recognized by the anti-fusion MAbs ; however, recognition was now primarily in the immature form and reduced during processing to the mature form. A model is discussed whereby gL binding gH at the N-terminal domain acts to draw together the C-terminal extracellular domain and this interaction affects a functional conformation during glycoprotein maturation.

Human Herpesvirus 6 Variant A Glycoprotein H-Glycoprotein L-Glycoprotein Q Complex Associates with Human CD46

“…Moreover, both MAbs against gH, 2E4 and 1D3, can neutralize virus infectivity and prevent polykaryocyte formation, with 2E4 acting more efficiently (2, 7). Therefore, 2E4 and 1D3 can be described as anti-fusion MAbs (2). Both of these MAbs recognize epitopes in the external domain of gH (2).…”

Interaction of Glycoprotein H of Human Herpesvirus 6 with the Cellular Receptor CD46

“…Of these, gH and gL appear to play prominent roles in the membrane fusion events that initiate HHV-6 infectivity, based on inhibitory activities of specific antibodies (7)(8)(9)(10)(11)(12). As in other herpesviruses, these glycoproteins form a heterodimeric complex, with gL being required for correct folding, intracellular maturation, and surface expression of gH (9,(12)(13)(14)(15)(16).…”

“…We also examined the effects of depleting two other HHV-6 glycoproteins, gp82-gp105 and gB; all three glycoproteins are known to play critical roles in viral infectivity, as shown by the neutralizing activities of specific antibodies to gH (7)(8)(9)(10)(11)(12), gB (17), or gp82-gp105 (19). We first analyzed the products of direct immunoprecipitation from the lysate of a mixture of HHV-6-infected HSB-2 cells and CD46-expressing NIH 3T3 cells (Fig.…”

“…Of these, gH and gL appear to play prominent roles in the membrane fusion events that initiate HHV-6 infectivity, based on inhibitory activities of specific antibodies (7-12). As in other herpesviruses, these glycoproteins form a heterodimeric complex, with gL being required for correct folding, intracellular maturation, and surface expression of gH (9,(12)(13)(14)(15)(16). Moreover, gB (the most highly conserved glycoprotein among herpesviruses) and another glycoprotein, gp82-gp105, (thus far found only in HHV-6 and the related ␤-herpesvirus, HHV-7) appear to be critical for the fusion/entry process, as specific antibodies against these proteins block both virus infectivity and syncytia…”

Complementation of the Function of Glycoprotein H of Human Herpesvirus 6 Variant A by Glycoprotein H of Variant B in the Virus Life Cycle

“…Anderson and Gompels showed previously that neutralizing antifusion antibodies could recognize the HHV-6 gH/gL complex in the absence of gQ1 and gQ2 (2).…”