Biophysical Society Conference | Estes Park 2023

Membrane Budding and Fusion

Tuesday Speaker Abstracts

STRUCTURAL AND FUNCTIONAL CHARACTERIZATION OF THE HERPES SIMPLEX VIRUS MEMBRANE FUSION REGULATOR, GH/GL

Gonzalo L Gonzalez-Del Pino 1 ; Richard Walsh 2 ; Gary Cohen 3 ; Katya Heldwein 1 ; 1 Tufts University, Molecular Biology and Microbiology, Boston, MA, USA 2 Harvard Medical School, CryoEM Facility, Boston, MA, USA 3 University of Pennsylvania, Basic & Translational Sciences, Philadelphia, PA, USA

Herpesviruses are highly successful pathogens that infect nearly all humans for life. Herpes simplex virus (HSV) is a prototypical alphaherpesvirus that causes mucocutaneous sores in most of the human population and life-threatening encephalitis in immunocompromised patients. Successful infection depends on fusion of the viral envelope with a host cell membrane, delivering the viral genome into the cell. This process requires three viral surface glycoproteins, gH, gL, and gB, that are conserved across herpesviruses. Large conformational rearrangements of gB, the trimeric viral fusogen, directly mediate the membrane fusion process. gH and gL form a heterodimer that regulates gB fusogenic activity and, in some cases, binds host receptors. Interaction sites between gH/gL and other HSV surface glycoproteins involved in fusion have been mapped using a panel of neutralizing antibodies. However, how gH/gL transmits the fusion activation signal from host receptors to gB is unknown. The objective of this work is to structurally characterize gH/gL in complex with a battery of neutralizing antibody fragments (Fabs) to uncover how it activates the viral fusogen, gB. Using electron cryomicroscopy, we have determined the structure of a gH/gL-Fab complex to pseudoatomic resolution. This structure has revealed remarkable flexibility in the hinge-like junction between the N- and C terminal modules. We have captured the glycoprotein-Fab complex in a range of conformational states where movements in the N-terminus and hinge-region of the heterodimer appear to be coupled to rearrangements of a helix-loop-helix motif in the C-terminus of gH/gL. This rearrangement happens on the face of gH/gL predicted to bind gB. The discovery of this concerted reorganization across the N- and C-terminal modules of gH/gL provides a potential mechanism for the transduction of a host-cell binding signal to activation of the fusogen, gB. These functional insights can translate to subunit-based vaccine and treatment options for currently untreatable herpes infections.

31