Mutational Analysis of the Hydrophobic Region of Herpes Simplex Virus-1 Glycoprotein gB

Abstract

The role of highly conserved amino acids within the carboxy-terminal hydrophobic domain of herpes simplex virus I (HSV-I) glycoprotein gB was studied by introducing point mutations using the method of site directed mutagenesis. A segment of this hydrophobic domain of glycoprotein gB contains a nuclear envelope (NE) targeting signal and the effect of these point mutations on targeting to the nuclear envelope was determined. A complementation assay was employed to determine the effect these mutations have on HSV-I infectivity .The point mutations created within the transmembrane domain of glycoprotein gB had no effect on nuclear envelope targeting and localization. However, single point mutations introduced into the first and second hydrophobic domains of glycoprotein gB, G₇₄₃R and F₇₇₀S, affected the targeting and localization of full-length glycoprotein gB at the nuclear envelope. When the transmembrane domain ofHSV-I glycoprotein gB containing the following point mutations A₇₉₀Q, A₇₉₁S, A₇₈₆S, A₇₈₆Y and A₇₉₀S, was introduced into a chimeric protein consisting of the cytoplasmic domain and ectodomain of a plasma membrane protein, vesicular stomatitis virus glycoprotein G, NE targeting and localization were affected. These point mutations may affect the targeting of glycoprotein gB by altering the structure of the targeting signal within the protein. It can be hypothesized that the presence of the cytoplasmic domain. ectodomain domain, and the first and second transmembrane domains within full-length glycoprotein gB can compensate for the effect these point mutations have on nuclear envelope targeting. since the same point mutations had no effect on the targeting · and localization of full-length glycoprotein gB. Complementation assays showed that the glycoprotein gB mutants, A₇₈₆S, A₇₈₆Y, A₇₈₆N, A₇₉₀Q, A₇₉₁S, F₇₇₀S, or G₇₄₃R, were unable to complement a gB-null virus even though these mutant proteins are localized at the nuclear envelope. These proteins may not have been incorporated into the viral capsid due to misfolding or due to the fact that sequences required for interaction with other viral proteins were lost. Another possibility is that the mutant proteins were incorporated into the HSV virion but were not biologically active.