Cross Talk among the Glycoproteins Involved in Herpes Simplex Virus Entry and Fusion: the Interaction between gB and gH/gL Does Not Necessarily Require gD

Abstract

ABSTRACT The gD, gB, and gH/gL glycoprotein quartet constitutes the basic apparatus for herpes simplex virus (HSV) entry into the cell and fusion. gD serves as a receptor binding glycoprotein and trigger of fusion. The conserved gB and gH/gL execute fusion. Central to understanding HSV entry/fusion has become the dissection of how the four glycoproteins engage in cross talk. While the independent interactions of gD with gB and gD with gH/gL have been documented, less is known of the interaction of gB with gH/gL. So far, this interaction has been detected only in the presence of gD by means of a split green fluorescent protein complementation assay. Here, we show that gB interacts with gH/gL in the absence of gD. The gB-gH/gL complex was best detected with a form of gB in which the endocytosis and phosphorylation motif have been deleted; this form of gB persists in the membranes of the exocytic pathway and is not endocytosed. The gB-gH/gL interaction was detected both in whole transfected cells by means of a split yellow fluorescent protein complementation assay and, biochemically, by a pull-down assay. Results with a panel of chimeric forms of gB, in which portions of the glycoprotein bracketed by consecutive cysteines were replaced with the corresponding portions from human herpesvirus 8 gB, favor the view that gB carries multiple sites for interaction with gH/gL, and one of these sites is located in the pleckstrin-like domain 1 carrying the bipartite fusion loop.