Based on genetic and antigenic differences and on their cell tropism, human herpes virus-6 (HHV-6) has been classified into two variants, HHV-6A and HHV-6B. Recently, these variants were re-classified as two different species. The HHV-6A glycoprotein complex, gH/gL/gQ1/gQ2 binds to its cellular receptor, CD46; however, the corresponding complex in HHV-6B rarely binds to CD46. To determine which viral molecules in the glycoprotein complex determine HHV-6A-CD46 binding, each molecule of the HHV-6A complex (i.e., gH, gL, gQ1, or gQ2) was replaced with the corresponding HHV-6B molecule, and the ability of the replaced protein to be incorporated into the complex and the ability of the complex to bind CD46 were examined. It was found that when all four glycoproteins were expressed, they were able to form a tetrameric complex. However, a complex formed by HHV-6A gH/gL/gQ1/gQ2 complexes replaced with HHV-6B gQ1 or gQ2 scarcely bind CD46, whereas HHV-6A complexes in which gH or gL was replaced with the HHV-6B molecules did bind it. These results indicate that HHV-6A gQ1 and gQ2 play an important role in CD46 binding.