Display of membrane proteins on the heterologous caveolae carved by caveolin-1 in the Escherichia coli cytoplasm

• Heterologous caveolae were formed inside E. coli through caveolin-1 expression.
• We tested targeting of co-expressed transmembrane proteins on the h-caveolae.
• The h-caveolae were ∼100 nm in diameter, and contained transmembrane proteins.
• The transmembrane proteins on the h-caveolae were functional and faced outward.
• Results provide a basis for exploiting the h-caveolae for biotechnological applications.

Caveolae are membrane-budding structures that exist in many vertebrate cells. One of the important functions of caveolae is to form membrane curvature and endocytic vesicles. Recently, it was shown that caveolae-like structures were formed in Escherichia coli through the expression of caveolin-1. This interesting structure seems to be versatile for a variety of biotechnological applications. Targeting of heterologous proteins in the caveolae-like structure should be the first question to be addressed for this purpose. Here we show that membrane proteins co-expressed with caveolin-1 are embedded into the heterologous caveolae (h-caveolae), the cavaolae-like structures formed inside the cell. Two transmembrane SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) proteins, Syntaxin 1a and vesicle-associated membrane protein 2 (VAMP2), were displayed on the h-caveolae surface. The size of the h-caveolae harboring the transmembrane proteins was ∼100 nm in diameter. The proteins were functional and faced outward on the h-caveolae. Multi-spanning transmembrane proteins FtsH and FeoB could be included in the h-caveolae, too. Furthermore, the recombinant E. coli cells were shown to endocytose substrate supplemented in the medium. These results provide a basis for exploiting the h-caveolae formed inside E. coli cells for future biotechnological applications.