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Nat Biotechnol. 2006 May;24(5):577-81. Epub 2006 Apr 30.

A fluorescent variant of a protein from the stony coral Montipora facilitates dual-color single-laser fluorescence cross-correlation spectroscopy.

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  • 1Laboratory for Cell Function and Dynamics, Advanced Technology Development Group, Brain Science Institute, RIKEN, 2-1 Hirosawa, Wako-city, Saitama, 351-0198, Japan.


Dual-color fluorescence cross-correlation spectroscopy (FCCS) is a promising technique for quantifying protein-protein interactions. In this technique, two different fluorescent labels are excited and detected simultaneously within a common measurement volume. Difficulties in aligning two laser lines and emission crossover between the two fluorophores, however, make this technique complex. To overcome these limitations, we developed a fluorescent protein with a large Stokes shift. This protein, named Keima, absorbs and emits light maximally at 440 nm and 620 nm, respectively. Combining a monomeric version of Keima with cyan fluorescent protein allowed dual-color FCCS with a single 458-nm laser line and complete separation of the fluorescent protein emissions. This FCCS approach enabled sensitive detection of proteolysis by caspase-3 and the association of calmodulin with calmodulin-dependent enzymes. In addition, Keima and a spectral variant that emits maximally at 570 nm might facilitate simultaneous multicolor imaging with single-wavelength excitation.

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