Budded baculovirus particle structure revisited

Abstract

Baculoviruses are a group of enveloped, double-stranded DNA insect viruses with budded (BV) and occlusion-derived (ODV) virions produced during their infection cycle. BVs are commonly described as rod shaped particles with a high apical density of protein extensions (spikes) on the lipid envelope surface. However, due to the fragility of BVs the conventional purification and electron microscopy (EM) staining methods considerably distort the native viral structure. Here, we use cryo-EM analysis to reveal the near-native morphology of two intensively studied baculoviruses, Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV) and Spodoptera exigua MNPV (SeMNPV), as models for BVs carrying GP64 and F as envelope fusion protein on the surface. The now well-preserved AcMNPV and SeMNPV BV particles have a remarkable elongated, ovoid shape leaving a large, lateral space between nucleocapsid (NC) and envelope. Consistent with previous findings the NC has a distinctive cap and base structure interacting tightly with the envelope. This tight interaction may explain the partial retaining of the envelope on both ends of the NC and the disappearance of the remainder of the BV envelope in the negative-staining EM images. Cryo-EM also reveals that the viral envelope contains two layers with a total thickness of ≈ 6-7 nm, which is significantly thicker than a usual biological membrane (<4 nm) as measured by X-ray scanning. Most spikes are densely clustered at the two apical ends of the virion although some envelope proteins are also found more sparsely on the lateral regions. The spikes on the surface of AcMNPV BVs appear distinctly different from those of SeMNPV. Based on our observations we propose a new near-native structural model of baculovirus BVs.

Quantification of the HIV‐1 virus‐like particle production process by super‐resolution imaging: From VLP budding to nanoparticle analysis

“…Although transiently produced VLPs in mammalian cells show lower productivities, the BEVS present a major bottleneck in product purity (Cervera et al, 2019). In fact, co‐purification between Gag VLPs and baculoviruses is of general concern, owing to their similar physicochemical and biochemical properties (Wang et al, 2016). Moreover, the concomitant production of EVs in both, mammalian and insect cells, including exosomes, microvesicles and apoptotic vesicles has to be carefully considered (González‐Domínguez, Gutiérrez‐Granados, Cervera, Gòdia, & Domingo, 2016; Thompson et al, 2015).…”

A Conserved Glycine Residue Is Required for Proper Functioning of a Baculovirus VP39 Protein

“…In the nucleocapsids, the viral genome is condensed by the protamine-like basic protein P6.9 and the capsid sheath is mainly composed of the VP39 protein (8). Homologs of both proteins are present in all baculoviruses that have been sequenced (9) and are known to be two of the three most abundant proteins in BVs of Autographa californica multiple nucleopolyhedrovirus (AcMNPV) (10).…”

Baculovirus as Versatile Vectors for Protein Display and Biotechnological Applications

“…More strikingly, the envelope proteins are located not only at one apical end, but are clustered at both polar ends (Fig. 11.6 and Wang et al, 2016). These findings indicate that foreign proteins displayed by GP64 fusion may be more abundant and not restricted to one apical end on the virus particle.…”

“…GP64 may still be the most frequently applied fusion partner for both virion and cell surface display strategies. By use of cryo-electron microscopy (cryo-EM), the baculovirus particle was shown to be an elongated ovoid shape with a lateral space between the envelope and nucleocapsid, rather than a rod-shaped particle (Wang et al, 2016). More strikingly, the envelope proteins are located not only at one apical end, but are clustered at both polar ends (Fig.…”