Reengineering cyt b562 for hydrogen production: A facile route to artificial hydrogenases

Abstract

Bioinspired, protein-based molecular catalysts utilizing base metals at the active are emerging as a promising avenue to sustainable hydrogen production. The protein matrix modulates the intrinsic reactivity of organometallic active sites by tuning second-sphere and long-range interactions. Here, we show that swapping Co-Protoporphyrin IX for Fe-Protoporphyrin IX in cytochrome b562 results in an efficient catalyst for photoinduced proton reduction to molecular hydrogen. Further, the activity of wild type Co-cyt b562 can be modulated by a factor of 2.5 by exchanging the coordinating methionine with alanine or aspartic acid. The observed turnover numbers (TON) range between 125 and 305, and correlate well with the redox potential of the Co-cyt b562 mutants. The photosensitized system catalyzes proton reduction with high efficiency even under an aerobic atmosphere, implicating its use for biotechnological applications. This article is part of a Special Issue entitled Biodesign for Bioenergetics--the design and engineering of electronic transfer cofactors, proteins and protein networks, edited by Ronald L. Koder and J.L. Ross Anderson.

Artificial Metalloenzymes: Reaction Scope and Optimization Strategies

“…Mutation of the coordinating methionine of a cobalt-substituted Cytochrome b562 (PDB code 1QPU) affords an artificial hydrogenase. 209 Artero and coworkers explored a similar strategy using cobalt complexes. Some advantageous aspects of artificial hydrogenases remain to be systematically explored.…”

Mimochrome, a metalloporphyrin‐based catalytic Swiss knife†

“…High overpotential values, low water-solubility, and the need for strong acids as proton sources are the common drawbacks associated with small-sized complexes [308][309][310]. On the other hand, cobalt-reconstituted heme-proteins, such as Mb and Cyt b562, have been shown to function in neutral water, but suffering from O 2 -intolerance and unsatisfactory TONs (up to 1,500) [311,312]. As an exception, cobalt-Cyt c552 from Hydrogenobacter thermophilus (Ht-CoM61A) displayed exceedingly high TON (270,000), albeit with a high overpotential value (730 mV) [313].…”

Rational design of metalloenzymes: From single to multiple active sites

“…As developed for more than 50 years, a powerful approach for designing artificial heme proteins is to reconstitute the apo-protein with heme b derivatives, such as heme analogs by modification with other substituents and replacement of the heme iron with other metal ions [129,130]. With the advantages of small size (153 amino acids and 1 heme), easy-to-purify and easy-to-characterize, Mb was favored for design of artificial metalloenzymes by this approach [25], as well as other heme proteins such as Cyt P450 [131] and Cyt b562 [132]. Recently, this old trick has afforded new achievements in design of metalloenzymes in Mb with advanced functions, as exemplified by following case studies.…”