Detailed Study of the Interaction between Human Herpesvirus 6B Glycoprotein Complex and Its Cellular Receptor, Human CD134

Abstract

Recently, we identified a novel receptor, CD134, which interacts with the human herpesvirus 6B (HHV-6B) glycoprotein (g)H/ gL/gQ1/gQ2 complex and plays a key role in the entry of HHV-6B into target cells. However, details of the interaction between the HHV-6B gH/gL/gQ1/gQ2 complex and CD134 were unknown. In this study, we identified a cysteine-rich domain (CRD), CDR2, of CD134 that is critical for binding to the HHV-6B glycoprotein complex and HHV-6B infection. Furthermore, we found that the expression of HHV-6B gQ1 and gQ2 subunits was sufficient for CD134 binding, which is different from the binding of human herpesvirus 6A (HHV-6A) to its receptor, CD46. Finally, we identified a region in gQ1 critical for HHV-6B gQ1 function. These results contribute much to our understanding of the interaction between this ligand and receptor. IMPORTANCEWe identified the domain in HHV-6B entry receptor CD134 and the components in the HHV-6B gH/gL/gQ1/gQ2 complex required for ligand-receptor binding during HHV-6B infection. Furthermore, we identified domains in gQ1 proteins of HHV-6A and -6B and a key amino acid residue in HHV-6B gQ1 required for its function. These data should be the basis for further investigation of ligand-receptor interaction in the study of HHV-6A and -6B. Shortly after its discovery, human herpesvirus 6 (HHV-6) was recognized as a single virus species comprised of two variants, HHV-6A and HHV-6B (1-4). Recently, HHV-6 variants have been reclassified as two virus species based on the different biocharacteristics of these two viruses with respect to the fields of biology, immunology, and epidemiology, and so on (5).One striking difference between HHV-6A and HHV-6B is their cell tropism. HHV-6A infects a wider range of cells than HHV-6B (5-7). Although determinants of viral cell tropism lie in each step of the virus life cycle in target cells, the differences in receptor preference of HHV-6A and -6B may contribute much to their cell tropism. Human CD46 was identified as the cell receptor for HHV-6 (8) and binds the HHV-6A gH/gL/gQ1/gQ2 complex (9, 10). Interestingly, we found that a similar glycoprotein complex exists in HHV-6B but does not bind to CD46 (11, 12), even though it shares a relatively high sequence identity with the glycoprotein in HHV-6A (especially the gH and gL components). Recently, we found that human CD134 is a specific cellular receptor for HHV-6B and binds to the HHV-6B gH/gL/gQ1/gQ2 complex (13). While CD46 is expressed on all nucleated cells (14, 15), CD134 is expressed mainly on activated T cells (16). The different expression profiles of these two cellular receptors may be one of the key determinants of the differences in cell tropism of HHV-6A and -6B. However, it is still unknown how these two similar viral ligands bind to different cellular receptors.Analysis of the receptor-ligand binding process would contribute not only to our understanding of the viral life cycle itself but also to the development of treatment methods to block the virus life cycle at the first step. M...

Humanization of Murine Neutralizing Antibodies against Human Herpesvirus 6B

“…In this study, we showed that the neutralizing activity of OHV-3 is weaker than that of KH-1. The reason would be that KH-1 recognizes gQ1, and gQ1 is directly responsible for CD134 binding (25).The direct binding of KH-1 to gQ1 of the gH/gL/gQ1/gQ2 complex could disturb the interaction of gQ1 with CD134, because the tetrameric complex with a gQ1 mutant that was not recognized by KH-1 could not bind to CD134 (18,25) (Fig. 7A).…”

Inherited chromosomally integrated HHV-6 demonstrates tissue-specific RNA expressionin vivothat correlates with increased antibody immune response

“…IE1A and IE1B are large (150 kDa) proteins involved in preventing type I Interferon synthesis and signaling (26, 27). Glycoproteins Q (Q1 and Q2) are part of a multiprotein assembly responsible for receptor binding and viral entry (28, 29). iciHHV-6A expression was noticeably higher in the brain in both the GTEx and MSBB datasets compared to iciHHV-6B (Figures 2 and 3).…”

Determinants of Human CD134 Essential for Entry of Human Herpesvirus 6B

“…We replaced these two residues with the homologous residues in mCD134 (K79D and R95L) and then examined the interaction between the CD134 mutants and the HHV-6B gH/gL/gQ1/gQ2 complex by immunoprecipitation with an anti-gH antibody followed by Western blotting (in our previous study, we confirmed that both immunoprecipitation and pulldown assays could be used for the analysis of the HHV-6 receptor-ligand interaction [10,11]). The interaction between the HHV-6B complex and hCD134 was detected when R95, but not K79, was mutated.…”

“…The HHV-6A ligand, glycoprotein H (gH)/gL/gQ1/gQ2 complex, binds to human CD46, a ubiquitously expressed molecule that may contribute to the relatively broad cell tropism of HHV-6A (6)(7)(8). In contrast, human CD134 (hCD134) is the specific receptor for HHV-6B (9,10).…”

“…We found that cysteine-rich domain 2 (CRD 2) of hCD134 is critical for HHV-6B ligand binding and that a key amino acid residue (E127) within HHV-6B gQ1 is required for its function. The E127Q mutation within HHV-6B gQ1 completely abolishes binding to hCD134; however, the homologous mutation (Q135E) in HHV-6A gQ1 does not enable it to bind to CD134, even though these two gQ1s share high amino acid sequence similarity (10). Interestingly, the E (glutamic acid) and Q (glutamine) residues have similar structures in terms of their side chains, although only glutamic acid has a negative electric charge under physiological conditions.…”