Fluorescent proteins are the priceless tools to conduct research on biological processes. But these proteins glow only when stimulated with an external light source, which can damage cells.
A research team led by RIKEN - research institution in Japan - has now developed an alternative imaging technique using luminescent proteins called 'nano-lanterns' that are powered by chemical energy rather than light.
Earlier attempts to use luminescent proteins for imaging foundered because their light is too dim to track quick changes inside cells. Instead, Yasushi Okada, Akira Takai and colleagues from the institute, in collaboration with the team of Takeharu Nagai from Osaka University, looked to nature for inspiration.
The sea pansy Renilla reniformis contains an enzyme known as Renilla luciferase (RLuc) that helps to oxidize a molecule called coelenterazine - a chemical reaction that produces a flash of blue light. A couple of years ago, Nagai's research team coupled a mutant form of RLuc with a yellow-green fluorescent protein called mVenus to generate a luminescent imaging agent.
Building on this work, Okada and his colleagues created two more coelenterazine-oxidizing luminescent agents using the same approach by coupling RLuc with cyan and orange fluorescent proteins. The resulting nano-lanterns are about 20 times brighter than natural RLuc. "The luminescent probes are bright enough to be detected with an iPhone camera," says Okada.
Okada acknowledges that the technique has limitations, but these challenges can be overcome. "Now, our goal is to create red nano-lanterns that could be useful for deep-tissue imaging," he notes.
The team is now developing microscopes for super-resolution luminescence imaging, and using the nano-lanterns to further analyze gene expression within single cells.