Biology: The structure of Luciferase

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Proteins play a fundamental role in the existence of living organisms. They are major contributors of cell structure and mobility, hormonal interaction, information exchange, and, most importantly, regulation of essential reactions. Enzymes are proteins that activate or inhibit the conversion of a substrate to a product. Often, enzymes catalyze reactions that are crucial for biological processes, but a few regulate other aspects of life, such as communication between a species. The enzyme luciferase catalyzes the reaction that allows fireflies to communicate with each other via emission of a yellow-green to yellow-orange colored light (Nakatsu, T. et al., 2006, 372). This reaction is a bioluminescence reaction, where chemical energy…show more content…
et al., 2006, 373). Researchers have taken a closer look at the structure of the active site that facilitates the bioluminescent reaction; they found the Arg218 residue plays a heavy role in the secure binding of luciferin. The guanidinium side chain of Arg218 is particularly responsible for binding with the benzothiazole ring of the luciferin substrate. Moreover, Arg218 establishes electrostatic interactions with the ground state product of the phenol group ionization of luciferin, yet Arg218 also stabilizes the final excited state phenolate ion of oxyluciferin (Branchini, B.R., Magyar, R.A., Murtiashaw, M.H., and Portier, N.C, 2001, 2415-2416). The proper binding of luciferin determines the color of the light emission and is dependent on the amount of rotation of the excited oxyluciferin molecule. To further understand the role of Arg218, researchers created a mutant enzyme without the Arg218 residue to determine its impact on substrate production. When researchers converted the Arg residue to Lys, there was a 15-fold increase in Km for luciferin; the Km value suggests the substrate binding affinity of the enzyme. The increase in Km shows that luciferase has a lowered affinity to bind with substrates. This shows that a manipulation of the Arg218 residue can affect the catalytic activity of the enzyme. Usually, the enzyme loses its high binding affinity with luciferin.
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