Applied Microbiology and Biotechnology, Vol.102, No.2, 655-666, 2018
RMCE-based insect cell platform to produce membrane proteins captured on HIV-1 Gag virus-like particles
Conformationally complex membrane proteins (MPs) are therapeutic targets in many diseases, but drug discovery has been slowed down by the lack of efficient production tools. Co-expression of MPs with matrix proteins from enveloped viruses is a promising approach to obtain correctly folded proteins at the surface of virus-like particles (VLPs), preserving their native lipidic environment. Here, we implemented a site-specific recombinase-mediated cassette exchange (RMCE) strategy to establish a reusable HIV-1 Gag-expressing insect cell line for fast production of target MPs on the surface of Gag-VLPs. The Sf9 cell line was initially tagged with a Gag-GFP-expressing cassette incorporating two flipase recognition target sites (FRTs), one within the fusion linker of Gag-GFP. The GFP cassette was afterwards replaced by a Cherry cassette via flipase (Flp) recombination. The fusion of Gag to fluorescent proteins enabled high-throughput screening of cells with higher Gag expression and Flp-mediated cassette exchange ability, while keeping the functionality of the VLP scaffold unaltered. The best cell clone was then Flp-recombinated to produce Gag-VLPs decorated with a human beta 2-adrenergic receptor (beta 2AR). Release of a fluorescently labeled beta 2AR into the culture supernatant was confirmed by immunoblotting, and its co-localization with Gag-VLPs was visualized by confocal microscopy. Furthermore, the differential avidity of beta 2AR-dsplaying Gag-VLPs versus "naked" Gag-VLPs to an anti-beta 2AR antibody measured by ELISA corroborated the presence of beta 2AR at the surface of the Gag-VLPs. In conclusion, this novel insect cell line represents a valuable platform for fast production of MPs in their native conformation, which can accelerate small-molecule and antibody drug discovery programs.
Keywords:Membrane proteins;GPCRs;Virus-like particles (VLPs);RMCE systems;Insect cell line development