Structure-Based Mutations in the Herpes Simplex Virus 1 Glycoprotein B Ectodomain Arm Impart a Slow-Entry Phenotype

Fan, Qing; Kopp, Sarah J.; Connolly, Sarah A.; Longnecker, Richard

The refolding of a fusion protein from a prefusion to a postfusion conformation requires energy. For herpesviruses, an interaction with gH/gL is proposed to destabilize the prefusion conformation of gB to trigger the conformational change that mediates fusion. Heat has been used previously as a surrogate trigger for several class I and III fusion proteins to transition from a prefusion to a postfusion conformation (29, (39) (40) (41) (42) (43) (44) (45) . To explore whether the defects in gB 3A fusion could be overcome by heat, the viral penetration rate was examined at an elevated temperature. At 37°C, penetration by the gB 3A viruses required more than 10 h of incubation with cells (Fig. 5) ; however, penetration was detectable after only 4 h at 40°C (Fig. 8) . Although heat may impact multiple stages of the HSV-1 infectious cycle, WT virus penetration was unaffected by the 40°C incubation. The absence of a nonspecific enhancement of WT virus penetration at 40°C suggests that heat partially rescued the cell penetration of the gB 3A virus by affecting the gB 3A protein.