Conservation of Glycoprotein H (gH) in Herpesviruses: Nucleotide Sequence of the gH Gene from Herpesvirus Saimiri

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Abstract
We present the nucleotide sequence of the glycoprotein H (gH) gene of herpesvirus saimiri (HVS), a representative of the T lymphotropic herpesviruses of New World monkeys, and compare the predicted amino acid sequence with sequences of homologous proteins from four human herpesviruses. The HVS gH gene is located within a block of genes encoding products conserved in all herpesvirus subgroups as represented by the human herpesviruses herpes simplex virus, varicella-zoster virus, cytomegalovirus and Epstein-Barr virus. In agreement with the biological grouping of HVS as a lymphotropic gammaherpesvirus, its gH amino acid sequence shows greatest similarity to that of the B lymphotropic Epstein-Barr virus, although the nucleotide sequences of their respective gH genes show little similarity given different G + C compositions of 31% and 54%. The similarity observed between the gH amino acid sequences of the two representative gammaherpesviruses is greater than that between the two human alphaherpesviruses varicella-zoster virus and herpes simplex virus. The members of the gH family range in size from 706 to 743 amino acid residues for the beta- and gammaherpesviruses, to 838 to 841 for the alphaherpesviruses, giving nonglycosylated precursors with Mr values of 78,322 to 93,651. The difference in size is due to heterogeneity in the poorly conserved N-terminal regions of the larger alphaherpesviruses compared to the smaller beta- and gammaherpesvirus molecules. Greatest similarity is observed in the C-terminal halves of the proteins including residues surrounding four conserved cysteine residues, a conserved N-linked glycosylation site (within the sequence NGTV) 13 to 18 residues proximal to the membrane-spanning sequences, and a short cytoplasmic domain of seven or eight residues for the beta- and gammaherpesviruses'' and 14 or 15 residues for the alphaherpesviruses'' gH. Thus, the representatives of all subgroups of herpesviruses, including those with a non-human host, encode gH homologues. Together with the observation that gH of these viruses are major targets for virus neutralization by antibody, this suggests that this glycoprotein family is essential among all herpesviruses and represents a major component involved in herpesvirus infectivity.