Fluorescent protein biological function

For a complete functional study of a biological pathway, it is often necessary to confirm the important protein interactions by in vivo experiments. This can be done by demonstrating protein localizations on a microscopic level, for instance, by tagging proteins with the green fluorescent protein or localizing them with antibodies and colloidal gold particles using an electron microscope. Additional, very specific biochemical experiments are often required to confirm the putative protein function. 

It should be noted that the dynamics studied by fluorescence methods is the dynamics of relaxation and fluctuations of the electric field. Dipole-orientational processes may be directly related to biological functions of proteins, in particular, charge transfer in biocatalysis and ionic transport. One may postulate that, irrespective of the origin of the charge balance disturbance, the protein molecule responds to these changes in the same way, in accordance with its dynamic properties. If the dynamics of dipolar and charged groups in proteins does play an important role in protein functions, then fluorescence spectroscopy will afford ample opportunities for its direct study. 

Olenych SG, Claxton NS, Ottenberg GK, Davidson MW. The fluorescent protein color palette. In Current Protocols in Cell Biology. Bonifacino JS, Dasso M, Harford JB, Lippincott-Schwartz J, Yamada KM, eds. 2006. John Wiley Sons, Inc. New York. Giepmans BN, Adams SR, Ellisman MH, Tsien RY. The fluorescent toolbox for assessing protein location and function. Science 2006 312 217-224. 

The log-normal distribution is also rather universal in the present cell, as demonstrated in the distribution of some proteins, measured by the degree of fluorescence [41]. Now, is this universality the final statement for cell statistical mechanics We have to be cautious here, since too universal laws may not be so relevant to biological function. In fact, chemicals that obey the log-normal distribution may have too large fluctuations to control some function. Some other mechanism to suppress the fluctuation may work in a cell. 

Barbara Campanini graduated cum laude in pharmaceutical chemistry and technologies, University of Parma in 1998. In 2002, she received her Ph.D. in molecular biology and pathology, University of Parma defending a dissertation on Structural determinants of the stability of the pyridoxal 5 -phosphate-dependent enzyme 0-acetylserine sulfhydrylase. Since 2006, she works as a research scientist at the University of Parma. Her research interests include the functional characterization of PLP-dependent enzymes involved in cysteine metabolism and the preparation of variants of the green fluorescent protein for structural and spectroscopic studies. 

The GFP from the jellyfish Aequorea victoria, although not an enzyme, has become widely used as a marker for gene expression and localization. Although the fluorophore of GFP is not technically a protein-derived cofactor, it is a protein-derived fluorophore. This is another example of posttranslational modifications, which endow amino acid residues with a new function. In this case, the new function is not one which assists in catalysis. Instead, the results of these posttranslational modifications create new fluorescent properties, which serve a different biological function. As with most of the protein-derived cofactors discussed earlier, the presence and identity of the fluorophore is not evident from the amino acid sequence of the protein. The structure of the GFP fluorophore and mechanism of its biosynthesis were deduced from structural analyses. The X-ray crystal structure of GFP revealed that the covalently bound fluorescent chromophore is derived from three adjacent amino acids, serine-tyrosine-glycine on the polypeptide chain (Figure 13). ... 

Clearly, the biological activity of fluorescent proteins is determined by their intrinsic ability to emit light after irradiation with a suitable excitation wavelength. However, despite the extensive use of these proteins as reporters in molecular biology during the last decade, the biological functions of these proteins in their respective host organisms still are not very well known. 

Clearly, further phylogenetic, physiological and ecological research is required to gain more insights into the biological function and significance of fluorescent proteins... 

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