Identification and characterization of glycoprotein gH of human herpesvirus-6

Abstract

Sequence analysis of an 8-kb BamHI-G DNA fragment from human herpesvirus-6 variant A strain GS (HHV-6A(GS)) has identified a gene encoding a glycoprotein homologous to glycoprotein gH of other herpesviruses and this gene was designated as HHV-6 gH (Josephs et al., J. Virol. 65, 5597). The open reading frame (ORF) of HHV-6A(GS) gH gene was amplified by polymerase chain reaction and was expressed as a trpE fusion protein in bacteria. Stable fusion protein was made only with constructs containing amino acids 15 to 469 of the ORF and this fusion protein was used to raise rabbit antisera. In the in vitro transcription-translation analysis of the gH gene, addition of microsomal membranes resulted in the processing of an unprocessed precursor to a polypeptide product of about 108 K. These in vitro-synthesized precursor and product forms were immunoprecipitated by the rabbit antibodies against the gH fusion protein. Rabbit anti-gH antibodies neutralized the infectivity of both HHV-6 variant A strain GS and variant B strain Z-29, and immunoprecipitation reactions identified a virion envelope-associated 102 K polypeptide as the glycoprotein gH of HHV-6 variants A and B. In addition to the 102 K glycoprotein, nonglycosylated polypeptides of about 58 and 164 K with different partial peptide maps were also consistently coimmunoprecipitated from [35S]methionine-labeled HHV-6A(GS)-infected cells, but not from HHV-6B(Z-29)-infected cells. The similarity in the molecular weights of glycoprotein gH among the two strains belonging to the two variant groups of HHV-6 and neutralization of infectivity of both groups by rabbit antibodies against HHV-6A(GS) gH suggests conserved functions of glycoprotein gH among the two variant groups of HHV-6.