PHOTOSYNTHETIC REACTION CENTER MAQUETTE

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Maquettes are simplified synthetic versions of protein based structures. Progress with de novo synthesis of peptides presents the opportunity to construct chemically simple peptides that incorporate biological redox sites, permitting us to view the molecular engineering involved in their assembly and to establish the minimal requirements for function of their highly complex natural counterparts. [CPP-?2]2 protein (CPP = coproporphyrin I, ? = CGGGELWKLHEELLKKFEELL-KLHEERLKKL-CONH2) is a maquette for the Photosynthetic Reaction Center (PRC) and consist of four identical amphipatic ?-helixes with a CPP dimeric unit appended covalently to the N terminus. It is based in our previous work (Nature 368, 425-432, 1994) and is able to bind up to four heme units. The dimeric porphyrin mimics the special pair in the PRC whereas the bis-His bound hemes are a model for Bchl and Bph. We are investigating the fluorescence emission properties of [CPP-?2]2 in buffer solution which has a fluorescence lifetime of 12.0 ns, a peak anisotropy of 0.06 and a rotational correlation time of 5.2 ns (?ex=398 nm and ?em =620 nm). In contrast, free-CCP in buffer exhibits a fluorescence emission 5 times greater (at the same OD as [CPP-?2]2)with a lifetime of 15.5 ns (30% longer) and a peak anisotropy of 0.14 and a rotational correlation time of 0.083 ns. These results indicate that we are indeed measuring the emission of CPP bound to the peptide and we could estimate a molecular diameter of 36 E assuming a spherical shape.