Toward deciphering biological phenomena by genetically-encoded molecular spies
Takeharu Nagai
Research Institute for Electronic Science, Hokkaido University, Japan
E-mail: tnagai@es.hokudai.ac.jp
HP: http://nano.es.hokudai.ac.jp/index.html

Our primary goal is to better understand how biological molecules function in space and time. To this end, we aredeveloping several techniques to visualize physiological events at molecular level in living cells and whole body. One
approach is the use of the green fluorescent protein and its derivatives (FPs) which are spontaneously fluorescent. To
expand color palette of FPs, we recently invented a pH-insensitive ultramarine fluorescent protein, Sirius, with enhanced
photostability and an emission peak at 424 nm, the shortest wavelength among fluorescent proteins reported to date. The
pH-insensitivity of Sirius makes possible prolonged visualization of biological events in an acidic environment.
Combination of FPs with fluorescence resonance energy transfer (FRET) technique allows us to develop functional
indicator, thereby we can visualize localized molecular events in their natural environment in vivo. For example, we havedeveloped an ultra-sensitive Ca2+ indicator by introducing some modification into Ca2+ sensing domain of YC3.60. Its
small Kd value (20 nM) allows us to detect Ca2+ dynamics even at 10-150 nM ranges without affecting cellular viability.
Large dynamic range (1400 %) also enables us to detect the signaling pattern in 100,000 cellular networks at single cellresolution, being the largest scales to be achieved so far. Furthermore, we applied the FRET technique to make aphotoconvertible fluorescent protein, Phamret, which can be highlighted by UV stimulation inducing a change influorescence emission from cyan to green color. Phamret can be monitored by single-excitation-dual-emission mode
allowing mobility analyses over a broad range of kinetics. In this seminar, I will introduce not only several kinds ofFP-based indicators mentioned above but also the use of autoluminescent indicators in conjunction with optogenetic
technology.
Selected references
1. Takemoto K et al. Chromophore-assisted light inactivation of HaloTag fusion proteins labeled with eosin in living cells.
ACS Chemical Biology 6: 401-406, 2011
2.

Horikawa K et al. Spontaneous network activity visualized by ultra-sensitive Ca2+ indicators, yellow cameloen-Nano.
Nature Methods 7, 729-732, 2010

3.

Saito K et al. Auto-luminescent genttically-encoded ratiometric indicator for real-time Ca2+ imaging at the single celllevel. PLoS ONE, 5: e9935，2010

4.

Kotera I et al. Reversible dimerization of Aequorea victoria fluorescent proteins increases the dynamic range ofFRET-based indicators. ACS Chem Biol. 5:215-222，2010

5.

Imamura H et al. Visualization of ATP levels inside single living cells with fluorescence resonance energy
transfer-based genetically encoded indicators. Proc. Natl, Acad, Sci. USA 106:15651-15656, 2009

6.

Tomosugi W et al. An ultramarine fluorescent protein with increased photostability and pH insensitivity.
Nature Methods 6: 351-353, 20097.

Saito K et al. A mercury arc lamp-based multi-color confocal real time imaging system for cellular structure andfunction. Cell Struct Funct. 33: 133-141, 20088.

Matsuda T et al. Direct measurement of protein dynamics inside cells using a rationally designed photoconvertible
protein. Nature Methods 5:339-345, 2008