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Faster Interprotein Electron Transfer in a [Myoglobin, b5] Complex with a Redesigned Interface

Science  19 Nov 2010:
Vol. 330, Issue 6007, pp. 1075-1078
DOI: 10.1126/science.1197054

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Speeding Electron Transfer Between Proteins

Compared to those observed in photosynthetic proteins, electron transfer rates between other large biomolecules, such as myoglobin and cytochrome b5, are very slow. Xiong et al. (p. 1075) show that modifying the acidic amino acid residues in the binding surface of myoglobin to lysine changes the distribution of structures to ones that favor faster electron transfer from the zinc porphyrin in myoglobin to the heme iron of cytochrome b5. The rates observed are within an order of magnitude of those observed for the initial step of charge separation in photosynthesis and provide valuable data for scientists interested in designing reactive proteins.

Abstract

Direct measurements of electron transfer (ET) within a protein-protein complex with a redesigned interface formed by physiological partner proteins myoglobin (Mb) and cytochrome b5 (b5) reveal interprotein ET rates comparable to those observed within the photosynthetic reaction center. Brownian dynamics simulations show that Mb in which three surface acid residues are mutated to lysine binds b5 in an ensemble of configurations distributed around a reactive most-probable structure. Correspondingly, charge-separation ET from a photoexcited singlet zinc porphyrin incorporated within Mb to the heme of b5 and the follow-up charge-recombination exhibit distributed kinetics, with median rate constants, Embedded Image = 2.1 × 109 second−1 and Embedded Image = 4.3 × 1010 second−1, respectively. The latter approaches that for the initial step in photosynthetic charge separation, k = 3.3 × 1011 second−1.

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