Lumazine protein is a highly fluorescent protein found in Photobacterium. The broad and long term goals of this program are to determine the three dimensional structure of lumazine protein, to characterize the interactions of this protein with various ligands, and to elucidate how this protein carries out its natural function as the emitter of bioluminescence in Photobacterium cells. The primary sequence of lumazine protein has been determined but all attempts to obtain X-ray diffraction quality crystals have failed. Therefore lumazine protein presents itself as a challenging problem in 2D-NMR structure methods being at the upper limit of mass (21 kD) feasible using this method. The primary sequence was determined by both chemical and genomic methods. Clones and probes for lumazine protein are therefore on hand thus enabling the sequences of natural variants to be quickly determined as well as single point mutations to be made. The natural ligand is 6,7-dimethyl-8-ribityllumazine and it is highly fluorescent both on and off the protein. It is non-covalently bound and may be replaced with other ligands satisfying certain steric requirements at the 8substituted position. This enables many spectral variants to be produced that can be studied from the point of view of ligand binding and bioluminescence properties. Major use can be made of a Picosecond Fluorescence system which is an NIH-University facility. It uses a sync-pumped Nd/YAG and dye laser, cavity dumped, as a 15-ps pulse excitation source. Lumazine protein-luciferase and lumazine protein-ligand interactions can readily determined by developed methods of fluorescence and anisotropy decay. Studies of energy transfer in the luciferase-lumazine protein complex are of particular relevance to the mechanism of bioluminescence excitation of lumazine protein.
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