Following his Ph.D., Tsien was a research fellow at
Gonville and Caius College, Cambridge, from 1977 to 1981. Beginning in 1989, he worked at the
University of California, San Diego, as professor of pharmacology and professor of chemistry and biochemistry, Tsien contributed to the fields of cell biology and neurobiology by discovering genetically programmable fluorescent tags, thereby allowing scientists to watch the behavior of molecules in living cells in real time. He also developed fluorescent indicators of
calcium ions and other ions important in biological processes. File:GFP Fluorescent Protein Movie.gif|thumb|420x420px|GFP Movie showing entire structure and zoom in to fluorescent chromophore. Movie created by Erik A. Rodriguez with UCSF Chimera from PDB: 1EMA in memory of Roger Y. Tsien for
Birch Aquarium. In 2004, Tsien was awarded the
Wolf Prize in Medicine "for his seminal contribution to the design and biological application of novel fluorescent and photolabile molecules to analyze and perturb cell signal transduction." In 2008, Tsien shared the Nobel Prize in Chemistry with
Osamu Shimomura and
Martin Chalfie for "the green fluorescent protein: discovery, expression and development."
Fluorescent proteins The multicolored
fluorescent proteins developed in Tsien's lab are used by scientists to track where and when certain genes are expressed in cells or in whole organisms. Typically, the gene coding for a protein of interest is fused with the gene for a fluorescent protein, which causes the protein of interest to glow inside the cell when the cell is irradiated with a suitable wavelength of light and allows microscopists to track its location in real time. This is such a popular technique that it has added a new dimension to the fields of molecular biology, cell biology, and biochemistry. Since the discovery of the
wild type GFP, numerous different mutants of GFP have been engineered and tested. The first significant leap forward was a
single point mutation (S65T) reported by Tsien in 1995 in
Nature. This mutation dramatically improved the fluorescent (both
intensity and
photostability) and spectral characteristics of GFP. A shift of the major excitation peak to 488 nm with the emission peak staying at 509 nm thus can be clearly observed, which matched very well the spectral characteristics of commonly available
FITC facilities. All these then largely amplified the practicality of using GFP by scientists in their research. Tsien mainly contributed to much of our understanding of how GFP works and for developing new techniques and mutants of GFP. Former trainees of Roger Y. Tsien include Atsushi Miyawaki and
Alice Y. Ting. Timelines of GFP-development involved by Tsien: • 2002: The critical structural difference between GFP and DsRed was revealed. One extra double-bond in the chromophore of DsRed extends its conjugation thus causes the red-shift. • 2002: Monomeric DsRed (mRFP) was first developed. • 2004: New "fruit" FPs were generated (by
in vitro and
in vivo directed evolutions). In 2009, a new kind of Infrared Fluorescent Protein (IFP) was developed by Tsien's group, and further reported and described by
Science. The new IFPs are developed from
bacterial phytochromes instead of from
multicellular organism like jellyfish. Under normal conditions, bacterial phytochromes absorb light for signaling instead of fluorescence, but they can be turned fluorescent after deleting some of the signaling parts by
genetic means such as
site-directed mutagenesis. In order to fluoresce, IFPs require an exogenous
chromophore,
biliverdin. In 2016, a new class of
fluorescent protein was evolved from a
cyanobacterial (
Trichodesmium erythraeum)
phycobiliprotein, α-
allophycocyanin, and named small ultra red fluorescent protein (
smURFP).
smURFP autocatalytically self-incorporates the
chromophore biliverdin without the need of an external
protein, known as a
lyase. Jellyfish- and
coral-derived fluorescent proteins require
oxygen and produce a
stoichiometric amount of
hydrogen peroxide upon
chromophore formation.
smURFP does not require
oxygen or produce
hydrogen peroxide and uses the
chromophore,
biliverdin.
smURFP has a large
extinction coefficient (180,000 M−1 cm−1) and has a modest
quantum yield (0.20), which makes it comparable biophysical brightness to
eGFP and ~2-fold brighter than most red or far-red
fluorescent proteins derived from
coral.
smURFP spectral properties are similar to the organic dye
Cy5.
Calcium imaging Tsien was a pioneer of
calcium imaging and known for developing various dyes which become fluorescent in the presence of particular ions such as calcium.
Aequorin is also a useful tool to indicate calcium level inside cells; however, it has some limitations, primarily is that its prosthetic group coelenterazine is consumed irreversibly when emits light, thus requires continuous addition of coelenterazine into the media. To overcome such issues, Tsien's group also developed the
calmodulin-based sensor, named
Cameleon.
FlAsH-EDT2 FlAsH-EDT2 is a biochemical method for specific covalent labeling of proteins harboring a tetracysteine motif (CCXXCC). It's a method based on recombinant protein molecules, and was developed by Tsien and his colleagues in 1998. • "FLASH-EDT2":
Fluorescein
ar
senical
helix binder,
bis-
EDT adduct, • "EDT": 1,2-ethanedithiol.
Fluorescence-assisted cancer surgery Mouse experiments by Tsien's group suggest that cancer surgery can be guided and assisted by fluorescent
peptides. The peptides are used as probes, and are harmless to living tissues and organs. Their lifetime in the body is only 4 or 5 days.
Clinical trials are awaited.
Industrial activities Tsien was also a notable biochemical inventor and held or coheld about 100 patents till 2010. In 1996, Tsien cofounded the Aurora Biosciences Corporation, which went public in 1997. In 2001, Aurora was acquired by the
Vertex Pharmaceuticals. Similarly, Tsien was also a scientific cofounder of
Senomyx in 1999. Tsien also promoted science education to promising young scientists through the first-ever San Diego Science Festival Lunch with a Laureate Program. == Personal life ==