Aerobic Photocatalytic H₂ Production by a [NiFe] Hydrogenase Engineered to Place a Silver Nanocluster in the Electron Relay

Abstract

Hydrogenase-1 (Hyd-1) from E. coli poses a conundrum regarding the properties of electrocatalytic reversibility and associated bidirectionality now established for many redox enzymes. Its excellent H2-oxidizing activity begins only once a substantial overpotential is applied, and it cannot produce H2. A major reason for its unidirectional behavior is that the reduction potentials of its electron-relaying FeS clusters are too positive relative to the 2H+/H2 couple at neutral pH; consequently, electrons held within the enzyme lack the energy to drive H2 production. However, Hyd-1 is O2-tolerant and even functions in air. Changing a tyrosine (Y) or threonine (T), located on the protein surface within 10 Å of the distal [4Fe-4S] and medial [3Fe-4S] clusters, to cysteine (C), allows site-selective attachment of a silver nanocluster (AgNC), the reduced or photoexcited state of which is a powerful reductant. The AgNC provides a new additional redox site, capturing externally supplied electrons with sufficiently high energy to drive H2 production. Assemblies of Y’227C (or T’225C) with AgNCs/PMAA (PMAA = polymethyl acrylate templating several AgNC) are also electroactive for H2 production at a TiO2 electrode. A colloidal system for visible-light photo-H2 generation is made by building the hybrid enzyme into a heterostructure with TiO2 and graphitic carbon nitride (g-C3N4), the resulting scaffold promoting uptake of electrons excited at the AgNC. Each hydrogenase produces 40 molecules of H2 per second and sustains 20% activity in air.

Thylakoid Membrane-Inspired Capsules with Fortified Cofactor Shuttling for Enzyme-Photocoupled Catalysis

“…Green biomanufacturing, which merges modern biotechnology and chemical technology for sustainable production of chemicals, has evolved as an indispensable route toward “carbon neutrality”. − Utilization of solar energy to drive biomanufacturing process could bring further benefits, such as lower energy consumption and higher efficiency, thus promoting the development of solar-powered biomanufacturing (SPBM). − As a typical SPBM, enzyme-photocoupled catalytic systems (EPCSs), which combine the natural enzyme with a library of semiconductor photocatalysts for solar-to-chemical conversion, − hold great promise in clean energy conversion and bulk chemical synthesis.…”

Panoramic insights into semi-artificial photosynthesis: origin, development, and future perspective

“…105 Therefore, a site-specific introduction of silver nanoclusters (AgNC) into the electron relay system of Hyd-1 offers a new way to energize them directly using visible light, which renders the hybrid system capable of producing H 2 under aerobic conditions. 106 On the other hand, to utilize the [FeFe]-H 2 ase with improved stability, the semi-synthetic H 2 ase was applied. Actually, [FeFe]-H 2 ase has the highest catalytic activity among different types of hydrogenases and a comparatively simple maturation, which contains the ''H-cluster'' verified by crystallography and spectroscopy.…”

Boosting the Performance of Formate Dehydrogenase by Silver Nanoclusters for Photoreduction of CO2 to Formate

“…The AgNC-sensitized TiO 2 can facilitate the monoxide dehydrogenase-catalyzed CO 2 -to-CO conversion, in which the turnover frequency (TOF) was increased by two orders of magnitudes compared to the AgNCs absent in the experiment . In the case of H 2 production catalyzed by the NiFe hydrogenase-1 from Escherichia coli, the light reaction and parallel electrochemical reduction showed that AgNCs could mediate energetic electrons directly into the enzyme molecules, turning the intrinsically non-H 2 producing enzyme into a mild H 2 producer in the presence of air . However, the exact mechanism of AgNC-facilitated enzymatic photocatalysis remains obscure and needs more in-depth investigation.…”