JoVE Logo
Faculty Resource Center

Sign In

Summary

Abstract

Introduction

Protocol

Representative Results

Discussion

Acknowledgements

Materials

References

Biochemistry

How to Quantify the Fraction of Photoactivated Fluorescent Proteins in Bulk and in Live Cells

Published: January 7th, 2019

DOI:

10.3791/58588

1Gynecologic Oncology Division, Stanford University School of Medicine

Here, we present a protocol that involves genetically coupled spectrally distinct photoactivatable and fluorescent proteins. These fluorescent protein chimeras permit quantification of the PA-FP fraction that is photoactivated to be fluorescent, i.e., the photoactivation efficiency. The protocol reveals that different modes of photoactivation yield different photoactivation efficiencies.

Photoactivatable and -convertible fluorescent proteins (PA-FPs) have been used in fluorescence live-cell microscopy for analyzing the dynamics of cells and protein ensembles. Thus far, no method has been available to quantify in bulk and in live cells how many of the PA-FPs expressed are photoactivated to fluoresce.

Here, we present a protocol involving internal rulers, i.e., genetically coupled spectrally distinct (photoactivatable) fluorescent proteins, to ratiometrically quantify the fraction of all PA-FPs expressed in a cell that are switched on to be fluorescent. Using this protocol, we show that different modes of photoactivation yielded different photoactivation efficiencies. Short high-power photoactivation with a confocal laser scanning microscope (CLSM) resulted in up to four times lower photoactivation efficiency than hundreds of low-level exposures applied by CLSM or a short pulse applied by widefield illumination. While the protocol has been exemplified here for (PA-)GFP and (PA-)Cherry, it can in principle be applied to any spectrally distinct photoactivatable or photoconvertible fluorescent protein pair and any experimental set-up.

In 2002, the first broadly applicable photoactivatable (PA-GFP1) and photoconvertible (Kaede2) fluorescent proteins were described. These optical highlighter fluorescent proteins change their spectral properties upon irradiation with UV-light, i.e., they become bright (photoactivatable fluorescent proteins, i.e., PA-FPs), or change their color (photoconvertible FPs). To date, several reversible and irreversible photoactivatable and photoconvertible fluorescent proteins have been developed3,4. In ensemble or bulk studies, optical highlighters hav....

Log in or to access full content. Learn more about your institution’s access to JoVE content here

1. Plasmid Construction

  1. Generate two-color fusion probes. Use a mammalian cell expression vector (see Table of Materials) in which mCherry112 and PA-mCherry113 have been inserted with the restriction sites AgeI and BsrGI.
  2. Order custom oligo-nucleotides to amplify the monomeric variants of eGFP and PA-eGFP containing the A206K mutation, i.e., mEGFP and PA-mEGFP14 without a stop codon as.......

Log in or to access full content. Learn more about your institution’s access to JoVE content here

The protocol presented here shows the ratiometric quantification of the fraction of fluorescent proteins that are photoactivated to be fluorescent (Figure 1). This fraction differs depending upon the mode of photoactivation.

A typical result using short time high-power photoactivation with a confocal laser scanning microscope (CLSM) is shown in Figure 2c. After titratin.......

Log in or to access full content. Learn more about your institution’s access to JoVE content here

So far, no method existed to determine in bulk the fraction of PA-FPs expressed in live cells that is photoactivated to be fluorescent. The presented protocol can be used for any spectrally distinct fluorescent protein pair. While exemplified here for the irreversible PA-FPs PA-GFP and PA-Cherry, this approach is in principle applicable to photoconvertible proteins as well. The spectrally distinct fluorescent protein, however, must be selected carefully to minimize spectral overlap given that photoconvertible fluorescent.......

Log in or to access full content. Learn more about your institution’s access to JoVE content here

We would like to thank the Dorigo laboratory and the Neuroscience Imaging Service at Stanford University School of Medicine for providing equipment and space for this project.

....

Log in or to access full content. Learn more about your institution’s access to JoVE content here

Name Company Catalog Number Comments
pEGFP-N1 mammalian cell expression vector Clontech
DMEM w/o phenol red Thermo Fisher Scientific 11054020
Trypsin w/o phenol red Thermo Fisher Scientific 15400054
L-Glutamine (200 mM) Thermo Fisher Scientific 25030081
HEPES Thermo Fisher Scientific 15630080
LabTek 8-well chambers #1.0 Thermo Fisher Scientific 12565470
Fugene 6 Promega E2691

  1. Patterson, G. H., Lippincott-Schwartz, J. A photoactivatable GFP for selective photolabeling of proteins and cells. Science. 297 (5588), 1873-1877 (2002).
  2. Ando, R., Hama, H., Yamamoto-Hino, M., Mizuno, H., Miyawaki, A. An optical marker based on the UV-induced green-to-red photoconversion of a fluorescent protein. Proceedings of the National Academy of Sciences of the United States of America. 99 (20), 12651-12656 (2002).
  3. Renz, M., Lippincott-Schwartz, J., Day, R. N., Davidson, M. W. Ch. 9. The Fluorescent Protein Revolution Series in Cellular and Clinical Imaging. , 201-228 (2014).
  4. Shcherbakova, D. M., Sengupta, P., Lippincott-Schwartz, J., Verkhusha, V. V. Photocontrollable fluorescent proteins for superresolution imaging. Annual Review of Biophysics. , 303-329 (2014).
  5. Betzig, E., et al. Imaging intracellular fluorescent proteins at nanometer resolution. Science. 313 (5793), 1642-1645 (2006).
  6. Hess, S. T., Girirajan, T. P., Mason, M. D. Ultra-high resolution imaging by fluorescence photoactivation localization microscopy. Biophysical Journal. 91 (11), 4258-4272 (2006).
  7. Henderson, J. N., et al. Structure and mechanism of the photoactivatable green fluorescent protein. Journal of the American Chemical Society. 131 (12), 4176-4177 (2009).
  8. Subach, F. V., et al. Photoactivation mechanism of PAmCherry based on crystal structures of the protein in the dark and fluorescent states. Proceedings of the National Academy of Sciences of the United States of America. 106 (50), 21097-21102 (2009).
  9. Wiedenmann, J., et al. EosFP, a fluorescent marker protein with UV-inducible green-to-red fluorescence conversion. Proceedings of the National Academy of Sciences of the United States of America. 101 (45), 15905-15910 (2004).
  10. Habuchi, S., Tsutsui, H., Kochaniak, A. B., Miyawaki, A., van Oijen, A. M. mKikGR, a monomeric photoswitchable fluorescent protein. PLoS One. 3 (12), e3944 (2008).
  11. McKinney, S. A., Murphy, C. S., Hazelwood, K. L., Davidson, M. W., Looger, L. L. A bright and photostable photoconvertible fluorescent protein. Nature Methods. 6 (2), 131-133 (2009).
  12. Shaner, N. C., et al. Improved monomeric red, orange and yellow fluorescent proteins derived from Discosoma sp. red fluorescent protein. Nature Biotechnology. 22 (12), 1567-1572 (2004).
  13. Subach, F. V., et al. Photoactivatable mCherry for high-resolution two-color fluorescence microscopy. Nature Methods. 6 (2), 153-159 (2009).
  14. Zacharias, D. A., Violin, J. D., Newton, A. C., Tsien, R. Y. Partitioning of lipid-modified monomeric GFPs into membrane microdomains of live cells. Science. 296 (5569), 913-916 (2002).
  15. Slocum, J. D., Webb, L. J. A Double Decarboxylation in Superfolder Green Fluorescent Protein Leads to High Contrast Photoactivation. Journal of Physical Chemistry Letters. 8 (13), 2862-2868 (2017).
  16. Subach, F. V., Patterson, G. H., Renz, M., Lippincott-Schwartz, J., Verkhusha, V. V. Bright monomeric photoactivatable red fluorescent protein for two-color super-resolution sptPALM of live cells. Journal of the American Chemical Society. 132 (18), 6481-6491 (2010).
  17. Renz, M., Wunder, C. Internal rulers to assess fluorescent protein photoactivation efficiency. Cytometry A. , (2017).
  18. Renz, M., Daniels, B. R., Vamosi, G., Arias, I. M., Lippincott-Schwartz, J. Plasticity of the asialoglycoprotein receptor deciphered by ensemble FRET imaging and single-molecule counting PALM imaging. Proceedings of the National Academy of Sciences of the United States of America. 109 (44), E2989-E2997 (2012).

This article has been published

Video Coming Soon

JoVE Logo

Privacy

Terms of Use

Policies

Research

Education

ABOUT JoVE

Copyright © 2024 MyJoVE Corporation. All rights reserved