Stabilization of Near-Infrared Fluorescent Proteins by Packaging in Virus-like Particles.

Near-IR fluorescent Qβ virus-like particles (VLPs) were produced in a high yield by packaging highly red-shifted monomeric and dimeric versions of biliverdin-dependent fluorescent proteins within the capsid shell. The simple addition of biliverdin hydrochloride to the medium during or after protein expression was enough to produce fully matured encapsidated fluorophores. The packaged near-IR proteins exhibited identical photochemical properties to their nonencapsidated analogues but were far more stable toward heat, chaotrope-induced denaturation, and proteolysis. Noninvasive imaging showed the VLPs to traffic primarily to the liver after systemic injection in mice, revealing that the particles were easily detected by a standard instrument.