Cairns Tina M, Friedman Lisa S, Lou Huan, Whitbeck J Charles, Shaner Marie S, Cohen Gary H, Eisenberg Roselyn J
Department of Microbiology, School of Dental Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
J Virol. 2007 May;81(10):5102-11. doi: 10.1128/JVI.00097-07. Epub 2007 Mar 7.
Glycoprotein H (gH) is conserved among all herpesviruses and is essential for virus entry and cell fusion along with gL, gB, and, in most alphaherpesviruses, gD. Within the gH/gL heterodimer, it is thought that gH accounts for the fusion function and gL acts as a chaperone for the folding and transport of gH. Here, we found that the N terminus of gH2 contains important elements involved in both its folding and its transport. Our conclusions are based on the phenotypes of a series of gH deletion mutants in which the signal sequence (residues 1 to 18) was retained and N-terminal residues were removed up to the number indicated. The first mutant, gH2Delta29 (deletion of residues 19 to 28), like wild-type (WT) gH, required gL for both transport and function. To our surprise, two other mutants (gH2Delta64 and gH2Delta72) were transported to the cell surface independent of gL but were nonfunctional, even when complexed with gL. Importantly, a fourth mutant (gH2Delta48) was transported independent of gL but was functional only when complexed with gL. Using a panel of monoclonal antibodies against gH2, we found that when gH2Delta48 was expressed alone, its antigenic structure differed from that of gH2Delta48/gL or gH2-WT/gL. Mutation of gH2 residue R39, Y41, W42, or D44 allowed gL-independent transport of gH. Our results also show that gL is not merely required for gH transport but is also necessary for the folding and function of the complex. Since gH2Delta64/gL and gH2Delta72/gL were nonfunctional, we hypothesized that residues critical for gH/gL function lie within this deleted region. Additional mutagenesis identified L66 and L72 as important for function. Together, our results highlight several key gH residues: R39, Y41, W42, and D44 for gH transport and L66 and L72 for gH/gL structure and function.
糖蛋白H（gH）在所有疱疹病毒中都很保守，与gL、gB一起对于病毒进入和细胞融合至关重要，并且在大多数α疱疹病毒中，还与gD有关。在gH/gL异源二聚体中，人们认为gH负责融合功能，而gL则作为gH折叠和转运的伴侣蛋白。在这里，我们发现gH2的N末端包含参与其折叠和转运的重要元件。我们的结论基于一系列gH缺失突变体的表型，这些突变体保留了信号序列（第1至18位氨基酸），并去除了直至所示编号的N末端氨基酸。第一个突变体gH2Delta29（缺失第19至28位氨基酸）与野生型（WT）gH一样，其转运和功能都需要gL。令我们惊讶的是，另外两个突变体（gH2Delta64和gH2Delta72）独立于gL转运到细胞表面，但无功能，即使与gL复合时也是如此。重要地，第四个突变体（gH2Delta48）独立于gL转运，但仅在与gL复合时才有功能。使用一组针对gH2的单克隆抗体，我们发现当单独表达gH2Delta48时，其抗原结构与gH2Delta48/gL或gH2-WT/gL的不同。gH2的R39、Y41、W42或D44位点发生突变可使gH实现不依赖gL的转运。我们的结果还表明，gL不仅是gH转运所必需的，也是该复合物折叠和功能所必需的。由于gH2Delta64/gL和gH2Delta72/gL无功能，我们推测对于gH/gL功能至关重要的氨基酸位于这个缺失区域内。进一步的诱变确定L66和L72对功能很重要。总之，我们的结果突出了几个关键的gH氨基酸位点：R39、Y41、W42和D44对gH转运很重要，而L66和L72对gH/gL的结构和功能很重要。
