Photonic proteins

A third class of photonic proteins is made up of those that evolved a Hght-emitting role, such as the green fluorescent protein (GFP) found in Aequorea (jellyfish) and ReniUa (sea pansy). In nature, GFP is excited through radiationless energy transfer by the well-known chemiluminescent protein aequorin, also found in Aequorea. Currently, little is known about the function of GFP as compared to the Hght signaling function of the extensively studied chemiluminescent firefly luciferase. ... 

In this chapter, we review the new and emerging field of engineering artificial photonic proteins, which complements the classic study of natural photoproteins discussed above. The term artificial photonic... 

In contrast to the previous discussion, some photonic protein switches are reversible. Reminiscent of several retinylidene-based rhodopsins, such as Sensory Rhodopsin most of these systems are based on reversible photoisomerization. In this case, however, the chromophore is based on the azobenzene, cinnamate, or spiropyrane-merocyanine system. The photochemical reactions for these three classes of photonic switches are illustrated in Figure 133.3. 

In addition to photonic switches, photonic proteins were engineered to contain fluorescent moieties that react to changes in a protein s local environment and to conformational changes. In this section, we review several examples of designing photonic probes that goes beyond simple chemical labeling and cysteine mutagenesis. 

In addition to chemical engineering and site-directed mutagenesis described in the previous section, an approach based on tRNA-mediated protein engineering (TRAMPE) presents new opportunities for engineering photonic proteins. TRAMPE reHes on the following ... 

Recent progress was made in all these areas (see Rothschild and Gite for a detailed review), and a few representative examples that resulted in the production of photonic proteins are described below. 

In addition to custom design of photonic proteins, which normally requires site-specific modifications at particular internal residues, TRAMPE can be used to incorporate photonic moieties at nonspecific positions, such as at random lysine residues or only at the N-terminal position of a protein. This approach can be useful in the fields of gene expression, proteomics, and even medical molecular diagnostics. For example, fluorescent labels can be used to monitor in vitro or even in vivo expression of proteins, to build arrays of proteins with which to detect specific protein-protein or drug-protein interactions, and even to detect genetic defects, which are expressed on the protein leveL... 

In the continuing endeavor to build photonic proteins evolve, cutting-edge progress in molecular biology, photochemistry, and photobiology will continue to be relied upon. 

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