Fluorescent proteins (FP) are revolutionizing practically all areas of life sciences. Cell targeting with FPs is much more specific than with non-genetically encoded fluorescing probes or markers, and is providing an incredible degree of precision with which process in living tissues can be studied. Starting with the green fluorescing protein, first introduced about 15 years ago, various types of blue-, yellow-, and red-fluorescing proteins have been extensively mutated and studied to create brighter and better probes. Two photon laser scanning microscopy is currently the method of choice for high resolution deep living tissue imaging. Naturally, there is substantial drive to adapt FPs for the two-photon microscopy. However, these efforts have been seriously hampered, so far, by the low cross section of two-photon absorption (2PA), which for currently known FPs is, C2 <102 GM. (1 Goeppert-Mayer = 10-50 cm4 s-1 photon-1). On the other hand, from numerous studies in other areas of physics and chemistry, it is well known that the 2PA cross sections may be as large as, C2 =103 -104 GM, including fluorescing molecules of the size and complexity comparable to that of FPs. Furthermore, extensive studies of the nonlinear absorption in various organic chromophores (again performed for different reasons) have revealed basic structure-to-property relationships that allow routinely increase the 2PA cross section by orders of magnitude. This proposal is a collaboration between a genetic engineering/fluorescence imaging group and a nonlinear spectroscopy/physical chemistry groups. We are addressing the issue of increasing the efficiency of FPs probes specifically for two-photon fluorescence imaging. Our main challenge comes from the fact (well known in 2PA spectroscopy community) that there is no straightforward relationship between the conventional (one-photon) brightness and the efficiency of two-photon excitation. We are proposing a series of experiments, which will:
(Aim 1 and 2) Identify the best two-photon FPs by quantifying the two-photon spectra and cross sections of a broad range of existing fluorescing proteins in a broad spectral range, from 550 to 1500 nm;
(Aims 3) Perform specific mutations on the charged amino acids in the surrounding protein cage, such that the 2PA efficiency is maximized by optimizing the strong local electric field at the chromophore location. The extensive preliminary data presented in this proposal strongly supports this hypothesis. We expect to increase the two-photon brightness up to 10-100 times, especially in the red- and near-IR range of excitation wavelengths. Public Health Relevance: This collaborative effort between biologists and physicists will resolve a long-standing obstacle in real- time deep tissue imaging due to insufficient two-photon efficiency of available genetically encoded markers. We are going to dramatically enhance the two-photon efficiency by introducing specific mutations in the protein cage, which will increase the two-photon cross section of the chromophore by up to two orders of magnitude.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM086198-02
Application #
7694286
Study Section
Special Emphasis Panel (ZRG1-BST-Q (51))
Program Officer
Deatherage, James F
Project Start
2008-09-30
Project End
2012-07-31
Budget Start
2009-08-01
Budget End
2010-07-31
Support Year
2
Fiscal Year
2009
Total Cost
$243,412
Indirect Cost
Name
Montana State University - Bozeman
Department
Physics
Type
Schools of Arts and Sciences
DUNS #
625447982
City
Bozeman
State
MT
Country
United States
Zip Code
59717
Wu, Jiahui; Liu, Lin; Matsuda, Tomoki et al. (2013) Improved orange and red Ca²± indicators and photophysical considerations for optogenetic applications. ACS Chem Neurosci 4:963-72
Drobizhev, Mikhail; Hughes, Thomas E; Stepanenko, Yuriy et al. (2012) Primary role of the chromophore bond length alternation in reversible photoconversion of red fluorescence proteins. Sci Rep 2:688
Drobizhev, M; Makarov, N S; Tillo, S E et al. (2012) Describing two-photon absorptivity of fluorescent proteins with a new vibronic coupling mechanism. J Phys Chem B 116:1736-44
Drobizhev, Mikhail; Makarov, Nikolay S; Tillo, Shane E et al. (2011) Two-photon absorption properties of fluorescent proteins. Nat Methods 8:393-9
Tillo, Shane E; Hughes, Thomas E; Makarov, Nikolay S et al. (2010) A new approach to dual-color two-photon microscopy with fluorescent proteins. BMC Biotechnol 10:6
Drobizhev, Mikhail; Tillo, Shane; Makarov, Nikolay S et al. (2009) Color hues in red fluorescent proteins are due to internal quadratic Stark effect. J Phys Chem B 113:12860-4
Drobizhev, M; Tillo, S; Makarov, N S et al. (2009) Absolute two-photon absorption spectra and two-photon brightness of orange and red fluorescent proteins. J Phys Chem B 113:855-9