Baculovirus envelope fusion proteins F and GP64 exploit distinct receptors to gain entry into cultured insect cells

Group II nucleopolyhedroviruses (NPVs), e.g. Helicoverpa armigera (Hear) NPV and Spodoptera exigua (Se) MNPV (multiple NPV), lack a GP64-like protein that is present in group I NPVs, e.g. Autographa californica (Ac)MNPV, but have an unrelated envelope fusion protein named F. Three AcMNPV viruses were constructed by introducing AcMNPV gp64, HearNPV f or SeMNPV f genes, respectively, into a gp64-negative AcMNPV bacmid. Sf21 cells were incubated with different amounts of inactivated budded virus to occupy receptors and were subsequently infected with a fixed amount of infectious virus to compete for attachment. The results suggest that GP64 and F act on their own and use different receptors, while the two different F proteins exploit the same receptor. Additionally, gp64-null AcMNPV pseudotyped with baculovirus F was, in contrast to GP64, unable to transduce mammalian cells, indicating that mammalian cells do not possess baculovirus F protein receptors despite the structural similarity of baculovirus F to vertebrate viral fusion proteins.