Bioengineering of Halobacterium sp. NRC-1 gas vesicle nanoparticles with GvpC fusion protein produced in E. coli

Gas vesicle nanoparticles (GVNPs) are hollow, buoyant prokaryotic organelles used for cell flotation. GVNPs are encoded by a large gas vesicle protein (gvp) gene cluster in the haloarchaeon, Halobacterium sp. NRC-1, including one gene, gvpC, specifying a protein bound to the surface of the nanoparticles. Genetically engineered GVNPs in the Halobacterium sp. have been produced by fusion of foreign sequences to gvpC. To improve the versatility of the GVNP platform, we developed a method for displaying exogenously produced GvpC fusion proteins on the haloarchaeal nanoparticles. The streptococcal IgG-binding protein domain was fused at or near the C-terminus of GvpC, expressed and purified from E. coli, and shown to bind to wild-type GVNPs. The two fusion proteins, GvpC3GB and GvpC4GB, without or with a highly acidic GvpC C-terminal region, were found to be able to bind nanoparticles equally well. The GVNP-bound GvpC-IgG-binding fusion protein was also capable of binding to an enzyme-linked IgG-HRP complex which retained enzyme activity, demonstrating the hybrid system capability for display and delivery of protein complexes. This is the first report demonstrating functional binding of exogenously produced GvpC fusion proteins to wild-type haloarchaeal GVNPs which significantly expands the capability of the platform to produce bioengineered nanoparticles for biomedical applications. KEY POINTS: • Haloarchaeal gas vesicle nanoparticles (GVNPs) constitute a versatile display system. • GvpC-streptococcal IgG-binding fusion proteins expressed in E. coli bind to GVNPs. • IgG-binding proteins displayed on floating GVNPs bind and display IgG-HRP complex.