Green Fluorescent Protein A Cell Biological Tool Biology Essay


Green Fluorescent Protein is found to be a protein of great excellence. The versatility of this protein is substantiated by the researches being carried out in exploring the protein in detail. This review gives a flavor of the most important uses and properties of this protein.


Green Fluorescent Protein as the name suggests is an eminent protein with 238 aminoacids. The jelly fish Aequorea victoria is found to be one of the major source of Green Fluorescent Protein.(Strachan and Read, 2004). The discovery of such a beneficial protein was due to the strenuous efforts of Osamu Shimomura and his co-workers.(Shimomura, 2005).

The Green Fluorescent protein was found to be a protein with very high utility and valuable functional property. A study on its properties revealed that there are a couple of reactions that make Green Fluorescent light emission possible.(Shimomura, 1979). It also plays a prominent role in the field of gene delivery(Buss et al., 2010) , regenerative medicine(Remy et al., 2010) and as a pH reporter.(Moseyko and Feldman, 2001).

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Looking on to the structure of GFP, it was found that GFP can not only form dimers but also monomers and it is the crystal growth condition that makes dimerization possible. The 11 beta-sheet barrel like structure of GFP and alpha helix running diagonally gave GFP the shape of a can. The structure of GFP covering a diameter of 24 Å and a height of 42 Å has a chromophore in the centre of 11 beta sheet, and linking by alpha helical structure gives it a cis-geometry (Zimmer, 2002). On a deeper excavation on the light emitted by the protein indicated that GFP emitted a blue light, and it is on exposure to UV light a green fluorescent ring was exhibited.(Shimomura, 2005). Investigating on the mystery behind the spectral shifts, there came two mechanisms, radiative(trivial) energy transfer and radiation less energy transfer that played a vital role in this context.(Ward, 2005). The spectra of wild type GFP (Aequorea protein) is quite difficult to comprehend where in normal solution, with increase in excitation wavelength, the emission wavelength decreases.(Tsien, 1998). A similar finding indicated that the excitation and emission spectra varies among species(Ward, 2005) and color diversification event in phylogenetic tree do not allow GFP like protein cloned from nonbioluminescent organisms to exhibit green color.(Matz et al., 2005).

In order to find out the extremely significant element of Aequorea victoria (avGFP) folding process, it is vital to perform systematic and extensive variations of chromophore as well as avGFP protein matrix.(Hoesl et al., 2010). An experimental finding of Hoesl indicated that transposing Tryptophan(Trp) with Tryptophan57(Trp57) the local physicochemical determinant responsible for structural and integrity of avGFP was determined.(Hoesl et al., 2010). The pH sensitivity of GFP is able to play a stupendous role in quantifying the organellar pH, which would be possible only on focusing GFP to exact destination.(Tsien, 1998). This statement could be supported by bringing out the utility of GFP as pH reporter where it is able to function as plant gene reporter system and thereby able to signify the alteration in cytoplasmic pH stimulated due to environment(Moseyko and Feldman, 2001). The discovery is getting into its peak as it is evident from the vital role that enhanced GFP plays as marker gene in corneal gene therapy.(Buss et al., 2010). A similar finding have indicated that GFP get expressed well in transgenic mice and it opens a pathway for regenerative medicine.(Remy et al., 2010). Another interesting finding was published by Cheng that GFP gene on mutation can fluoresce brighter and such mutated marker gene is now forming an inevitable tool for observing gene expression in mammalian cells. (Cheng et al., 1996).These articles speak out that a lot of research is being carried out to analyze the relevance of GFP in field of gene delivery, gene expression and medicine.


GFP variants has been distributed into 7 classes with first four derived from polypeptides with Tyr at position 66 and 5 to 7 derived from Trp, His, Phen. The positioning of aminoacids is found to be the same in all 7 classes. The class 1 variant (wild type mixture of neutral phenol and anionic phenolate) show high stability and fluorescent capacity at low temperature. The class 2 variant (phenolate anion) indicates a tremendous combination of high brightness with simple excitation and emission spectra. Class 3 variant (neutral phenol) is expedient in supporting laser action and class 4 variant (YFP) is marketed as a Bio Yellow variety. Class 5 variant (indole) performs well only under mutation. Though class 6 variant (imidazole) forms the building block of functional dyes its activity is reduced by protein bleaching. Class 7 variant (phenyl) has not been well explored. (Tsien, 1998)

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Though GFP plays an important role as pH reporter due to pH sensitivity, there is an exigency to identify the mutations that eliminate molecular mechanisms of environmental modulations.(Tsien, 1998). There is also a requirement to look into the folding of GFP in detail and also the organisms that can be targeted other than Aequorea victoria.(Tsien, 1998)


To conclude GFP is definitely a phenomenal protein with a wide variety of uses. There use in the field of gene therapy, regenerative medicine is a new insight and a great contribution to field of medicine. A look through these articles indicates that the graph of GFP shows a hike, signifying the progression of research being carried out in this field.