Use of the green fluorescent protein and its mutants in quantitative fluorescence microscopy

George H. Patterson, Susan M. Knobel, Wallace D. Sharif, Steven R. Kain, David W. Piston

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Abstract

We have investigated properties relevant to quantitative imaging in living cells of five green fluorescent protein (GFP) variants that have been used extensively or are potentially useful. We measured the extinction coefficients, quantum yields, pH effects, photobleaching effects, and temperature-dependent chromophore formation of wtGFP, αGFP (F99S/M153T/V163A), S65T, EGFP (F64L/S65T), and a blue-shifted variant, EBFP (F64L/S65T/Y66H/Y145F). Absorbance and fluorescence spectroscopy showed little difference between the extinction coefficients and quantum yields of wtGFP and αGFP. In contrast, S65T and EGFP extinction coefficients made them both ~6-fold brighter than wtGFP when excited at 488 nm, and EBFP absorbed more strongly than the wtGFP when excited in the near-UV wavelength region, although it had a much lower quantum efficiency. When excited at 488 nm, the GFPs were all more resistant to photobleaching than fluorescein. However, the wtGFP and αGFP photobleaching patterns showed initial increases in fluorescence emission caused by photoconversion of the protein chromophore. The wtGFP fluorescence decreased more quickly when excited at 395 nm than 488 nm, but it was still more photostable than the EBFP when excited at this wavelength. The wtGFP and αGFP were quite stable over a broad pH range, but fluorescence of the other variants decreased rapidly below pH 7. When expressed in bacteria, chromophore formation in wtGFP and S65T was found to be less efficient at 37°C than at 28°C, but the other three variants showed little differences between 37°C and 28°C. In conclusion, no single GFP variant is ideal for every application, but each one offers advantages and disadvantages for quantitative imaging in living cells.

Original languageEnglish
Pages (from-to)2782-2790
Number of pages9
JournalBiophysical Journal
Volume73
Issue number5
DOIs
StatePublished - 1997

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