Faster Interprotein Electron Transfer in a [Myoglobin, b ₅ ] Complex with a Redesigned Interface

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, kfs=2.1×109second−1 and kbs=4.3×1010second−1, respectively. The latter approaches that for the initial step in photosynthetic charge separation, k = 3.3 × 1011 second−1.

The key role of water in the dioxygenase function of Escherichia coli flavohemoglobin

“…In most cases reduction is performed by another protein (the electron donor) that reduces the heme through interprotein ET. For the extensively studied mammalian Mb and Hb the reduction partner is Cytochrome-b5 (Cb5) another small heme protein [35][36][37]65]. An interesting question then arises as if the electron entry point to the globin domain is similar in interprotein (Mb/Cb5) and intraprotein (GD/FBD) ET.…”

“…Our results show that in FHb the electron enters the GD through the heme propionates. Interestingly, the results for the Mb/Cb5 show that best ET paths are those were electrons enter directly to Mb though the heme exposed edge which includes the propionates [35][36][37]65]. Although so far only these two cases have been analyzed and there is a complete lack of knowledge of many globin (particularly bacterial globins) reduction partners, it is tempting to propose that redox partners should dock close to the heme exposed edges for efficient ET to occur.…”

“…Then one electron from the reduced Flavin will reduce the heme, while remaining in the semi reduced radical state, until the heme is oxidized after an NOD cycle. FHbs are thus unique globins, since reduction involves an intra-protein ET between domains, and not inter-protein ET, as is the case for Mb and Hb reduction by Cytochrome-b5 [35][36][37]. Although understanding how structure, dynamics and domain-domain interactions in FHbs modulate ET could give insights into general reduction mechanisms of globins, the molecular details of the ET process in FHbs are still unknown.…”

Dynamics in transient complexes of redox proteins

“…This result indicates that the fraction of electron transfer active orientations of Cb5 could be increased dramatically, meaning that rather than sampling most of the Mb surface, Cb5 probes a smaller area in the region where fast electron transfer is possible. In a follow-up study [15,16], this effect was further improved by creating a positively charged patch around the porphyrin in Mb. In that mutant, not only is the electron transfer much faster, but also the affinity has increased, suggesting a shift in the equilibrium from the encounter state (Dynamic Docking model) to a well-defined state (Simple Docking model), similar to what was observed for the T12A mutation in the Cc-CcP described above.…”

Dynamic electron localization initiated by particle-bath coupling

“…The techniques developed here may have application in photo-induced electron transfer [30][31][32] , and photo-generation and transfer of charge in softer materials. Femtosecond electron transfer and energy relaxation from copper into a surface layer covered with ice (image potential band) has been well studied experimentally 33 .…”