Heldwein, E. | Search bioRxiv

bioRxiv2020

Structural basis for capsid recruitment and coat formation during HSV-1 nuclear egress

During herpesvirus infection, egress of nascent viral capsids from the nucleus is mediated by the viral nuclear egress complex (NEC). NEC deforms the inner nuclear membrane (INM) around the capsid by forming a hexagonal array. However, how the NEC coat interacts with the capsid and how curved coats are generated to enable budding is yet unclear. Here, by structure-guided truncations, confocal microscopy, and cryoelectron tomography, we show that binding of the capsid protein UL25 promotes the formation of NEC pentagons rather than hexagons. We hypothesize that during nuclear budding, binding of UL25 situated at the pentagonal capsid vertices to the NEC at the INM promotes formation of NEC pentagons that would anchor the NEC coat to the capsid. Incorporation of NEC pentagons at the points of contact with the vertices would also promote assembly of the curved hexagonal NEC coat around the capsid, leading to productive egress of UL25-decorated capsids.

microbiology↗

bioRxiv2020

Contributions of the four essential entry glycoproteins to HSV-1 tropism and the selection of entry routes.

Herpes Simplex viruses (HSV-1 and HSV-2) encode up to 16 envelope proteins, four of which are essential for entry. However, whether these four proteins alone are sufficient to dictate the broad cellular tropism of HSV-1 and the selection of different cell-type dependent entry routes is unknown. To begin addressing this, we previously pseudotyped VSV, lacking its native glycoprotein G, with only the four essential entry glycoproteins of HSV-1: gB, gH, gL, and gD. This novel VSV{Delta}G-BHLD pseudotype recapitulated several important features of HSV-1 entry: the requirement for gB, gH, gL, gD, a cellular receptor, and sensitivity to anti-gB and anti-gH/gL neutralizing antibodies. However, due to the use of a single cell type in that study, the tropism of the VSV{Delta}G-BHLD pseudotype was not investigated. Here, we show that the cellular tropism of the pseudotype is severely limited compared to wild-type HSV-1 and that its entry pathways differ from the native HSV-1 entry pathways. To test the hypothesis that other HSV-1 envelope proteins may contribute to HSV-1 tropism, we generated a derivative pseudotype containing the HSV-1 glycoprotein gC (VSV{Delta}G-BHLD-gC) and observed a gC-dependent increase in entry efficiency in two cell types. We propose that the pseudotyping platform developed here has the potential to uncover functional contributions of HSV-1 envelope proteins to entry in a gain-of-function manner. ImportanceHerpes simplex viruses (HSV-1 and HSV-2) contain up to 16 different proteins in their envelopes. Four of these, glycoproteins gB, gD, gH, and gL, are termed essential with regard to entry whereas the rest are typically referred to as non-essential based on the entry phenotypes of the respective single genetic deletions. However, the single-gene deletion approach, which relies on robust loss-of-function phenotypes, may be confounded by functional redundancies among the many HSV-1 envelope proteins. We have developed a pseudotyping platform, in which the essential four entry glycoproteins are isolated from the rest, which can be added back individually for systematic gain-of-function entry experiments. Here, we show the utility of this platform for dissecting the contributions of HSV envelope proteins, both the essential four and the remaining dozen (using gC as an example), to HSV entry.

microbiology↗