Direct Electron Transfer of Enzymes Facilitated by Cytochromes

Abstract

The direct electron transfer (DET) of enzymes has been utilized to develop biosensors and enzymatic biofuel cells on micro‐ and nanostructured electrodes. Whereas some enzymes exhibit direct electron transfer between their active‐site cofactor and an electrode, other oxidoreductases depend on acquired cytochrome domains or cytochrome subunits as built‐in redox mediators. The physiological function of these cytochromes is to transfer electrons between the active‐site cofactor and a redox partner protein. The exchange of the natural electron acceptor/donor by an electrode has been demonstrated for several cytochrome carrying oxidoreductases. These multi‐cofactor enzymes have been applied in third generation biosensors to detect glucose, lactate, and other analytes. This review investigates and classifies oxidoreductases with a cytochrome domain, enzyme complexes with a cytochrome subunit, and covers designed cytochrome fusion enzymes. The structurally and electrochemically best characterized proponents from each enzyme class carrying a cytochrome, that is, flavoenzymes, quinoenzymes, molybdenum‐cofactor enzymes, iron‐sulfur cluster enzymes, and multi‐haem enzymes, are featured, and their biochemical, kinetic, and electrochemical properties are compared. The cytochromes molecular and functional properties as well as their contribution to the interdomain electron transfer (IET, between active‐site and cytochrome) and DET (between cytochrome and electrode) with regard to the achieved current density is discussed. Protein design strategies for cytochrome‐fused enzymes are reviewed and the limiting factors as well as strategies to overcome them are outlined.

Direct Electrochemical Enzyme Electron Transfer on Electrodes Modified by Self-Assembled Molecular Monolayers

“…Catalysts 2020, 10, x FOR PEER REVIEW 7 of 26 molecule. Many oxidoreductases furthermore rely on cytochrome domains or subunits as "built-in" ET relays between the catalytically active cofactor and the electrode surfaces and will be discussed in the following sub-sections [100]. Reproduced with permission from [64].…”

“…Heme 3c Overall, these reports highlight cyt c as a core electron carrier enabling efficient ET between redox enzymes and the electrode surface across suitably chosen SAMs and along with the blue ET protein azurin as a case for characterization in unique detail, right down to the level of the single molecule. Many oxidoreductases furthermore rely on cytochrome domains or subunits as "built-in" ET relays between the catalytically active cofactor and the electrode surfaces and will be discussed in the following sub-sections [100].…”

Nanocatalysts Containing Direct Electron Transfer-Capable Oxidoreductases: Recent Advances and Applications

“…Those facts demonstrate that, for a successful DET, the enzyme should have distinctive features ensuring the electron transfer capabilities. Moreover, efficient DET, where enzymatic turnover is not limited by the rate of electron transfer, is rarely observed [53], and thus causes additional problems for a fast and sustainable DET-based electrocatalysis. In the next section, we will briefly review the principles of the DET and contemporary application of DET-capable oxidoreductases.…”

“…The enzyme transfers electrons from one of the substrates to another according to the reaction thermodynamics, that is, the electrons are transferred to a compound with higher redox potential [50]. Typically, oxidoreductases reduce coenzymes (i.e., NAD + , FAD, PQQ) to drive the oxidative reaction [51][52][53]; however, in recent years, artificial electron transfer mediators have also been synthesized and applied as electron accepting/donating substrates [54][55][56]. As illustrated in Figure 1A, for the oxidative process, those electroactive and low molecular mass mediators act as electron transport shuttles from/to the electrode and oxidoreductase and result in MET.…”

Cytochrome c-multiwalled carbon nanotube and cobalt metal organic framework/gold nanoparticle immobilized electrochemical biosensor for nitrite detection

“…16,17 However, it has been reported that electron transfer between electrode and Cyt c is difficult to achieve, because the active center of the enzyme is deeply embedded in the protein. [18][19][20] Meanwhile, the direct modication of enzyme to the electrode surface can lead to the loss of enzyme activity aer curing in a rigid environment. To overcome the above challenges, new materials were used to combine with Cyt c to modify the electrode, which can provide good microenvironment for the electron transfer of enzymes.…”