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

Abstract

bWe identified two key amino acid residues within human CD134 (hCD134) that are required for its interaction with human herpesvirus 6B (HHV-6B) and for HHV-6B entry into cells. One of the residues (K79) allows access of the HHV-6B ligand to hCD134. Murine CD134 (mCD134) functioned as an HHV-6B receptor when these two amino acid residues were replaced with homologous human residues. This study identifies both the HHV-6B receptor-ligand interaction and the species-specific determinants of hCD134 essential for HHV-6B entry. Human herpesvirus 6B (HHV-6B) is a betaherpesvirus. Initially, HHV-6B and HHV-6A were classified as two variants of HHV-6; however, they are now classified as two virus species due to their different bio-characteristics (1-5). One of the striking differences between these two viruses is receptor ligand usage. 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 (6-8). In contrast, human CD134 (hCD134) is the specific receptor for HHV-6B (9, 10).In a previous study, we performed a detailed analysis of the interaction between the HHV-6B ligand and its cellular receptor, hCD134. 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. These results led us to speculate that the negative electric charge of E might be important for HHV-6B gQ1 function and that there should be a corresponding residue(s) with a positive electric charge in hCD134 (most likely in the CRD 2 domain) that facilitates the interaction between hCD134 and the HHV-6B ligand. To test this, we focused on two amino acid residues in the CRD 2 domain of hCD134 (K79 and R95), both of which have a positive electric charge; neither of these residues is conserved in murine CD134 (mCD134) (Fig. 1A). Also, mCD134 did not interact with the HHV-6B gH/gL/gQ1/gQ2 complex (Fig. 1E).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. Since K79 is located within the loop structure of...

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Inflammatory Cytokine-Producing Cells and Inflammation Markers in the Synovium of Osteoarthritis Patients Evidenced in Human Herpesvirus 7 Infection

“…Previous studies have explored the molecular mechanisms of the cell entry of betaherpesviruses; some authors have designated CD46 as an entry receptor in the case of HHV-6 infection and demonstrated the presence of it on a major target cell—activated T lymphocytes [ 40 ]. Alternatively, other authors have explored CD134, which is a receptor specific for HHV-6B, belonging to the TNF receptor superfamily and expressed on activated CD4-positive T cells [ 41 , 42 , 43 ].…”

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