New Fluorescent Protein for Medical Imaging Found in Fishtank

An interesting development that comes from an unusual source, may soon help doctors see all those tumors much more clearly.

The development of the red fluorescent protein, which the researchers call Katushka, was reported by Howard Hughes Medical Institute international research scholars Andrey Zaraisky, Sergey A. Lukyanov, and their colleagues August 26, 2007, in the online version of Nature Methods. Principal development of Katushka was carried out by Dmitry Chudakov and colleagues in Lukyanov’s laboratory at the Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry in Moscow. Zaraisky and his colleagues are also at the institute.
According to the researchers, Katushka solves a major problem in the field of fluorescent reporter proteins. Fluorescent proteins have become invaluable research tools for labeling specific genes and tissues. This labeling permits researchers to follow gene activity visually or to track cellular development. However, there is no tracer that glows brightly in a particular “window” of the far-red spectrum favorable for maximally penetrating living tissues. Thus, such proteins were not practical for optically imaging tagged genes, cells or tissues in whole animals.
The development of Katushka might never have happened had it not been for the shrewd bargaining of Lukyanov. Visiting a Moscow pet shop, Lukyanov saw a brilliant red sea anemone among the denizens of the store’s aquarium. Sensing that the vivid red coloring in the anemone might provide the blueprint for a new biological tracer, he tried to buy the anemone. He was told by the shopkeeper that it had already been sold, and the buyer was expected shortly. Unfazed, Lukyanov persistently outbid the buyer and procured the creature.
Back in Lukyanov’s laboratory, Chudakov and his coworkers isolated the red protein from the anemone and then developed an enhanced version, which they named turbo red fluorescent protein (TurboRFP). The protein comprised a string of identical protein subunits, so the researchers also developed a single-unit monomeric version, which they called TagRFP.
Although TurboRFP was twice as bright as a comparable red protein, DsRed2, the researcher set out to improve its brightness in the far-red window. They created about 100,000 variants of the gene for TurboRFP, screening the resulting proteins for high brightness in the near-infrared. This screening yielded a highly bright variant protein, which they further optimized by randomly mutating the gene and selecting the brightest protein. They named this protein Katushka, a Russian diminutive for the name Ekaterina – after co-author Ekaterina Merzlyak, in recognition of her work developing TurboRFP and TagRFP. Katushka proved to be up to 10-fold brighter in the far-red, compared to the spectrally close fluorescent proteins HcRed and mPlum. mPlum was developed in 2004 by HHMI investigator Roger Y. Tsien at the University of California, San Diego, a leader in the study of fluorescent proteins for cell biology research. The researchers also generated a monomeric version of Katushka, called mKate, which is useful for molecular labeling of proteins.

Howard Hughes Medical Institute: New Red Fluorescent Protein a Glowing Success …
Image Caption: “Transgenic 2.5 month old Xenopus laevis expressing Katushka (left) and DsRed-Express (right) under the control of muscle actin promoter. The frogs are shown from the dorsal side under white light.”