Faster interprotein electron transfer in a [myoglobin, b₅] complex with a redesigned interface

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, k_f ^s = 2.1 × 10⁹ second^-1 and k _b^s = 4.3 × 10¹⁰ second^-1, respectively. The latter approaches that for the initial step in photosynthetic charge separation, k = 3.3 × 10¹¹ second^-1.