Controlling Redox Enzyme Orientation at Planar Electrodes

Abstract

Abstract:Redox enzymes, which catalyze reactions involving electron transfers in living organisms, are very promising components of biotechnological devices, and can be envisioned for sensing applications as well as for energy conversion. In this context, one of the most significant challenges is to achieve efficient direct electron transfer by tunneling between enzymes and conductive surfaces. Based on various examples of bioelectrochemical studies described in the recent literature, this review discusses the issue of enzyme immobilization at planar electrode interfaces. The fundamental importance of controlling enzyme orientation, how to obtain such orientation, and how it can be verified experimentally or by modeling are the three main directions explored. Since redox enzymes are sizable proteins with anisotropic properties, achieving their functional immobilization requires a specific and controlled orientation on the electrode surface. All the factors influenced by this orientation are described, ranging from electronic conductivity to efficiency of substrate supply. The specificities of the enzymatic molecule, surface properties, and dipole moment, which in turn influence the orientation, are introduced. Various ways of ensuring functional immobilization through tuning of both the enzyme and the electrode surface are then described. Finally, the review deals with analytical techniques that have enabled characterization and quantification of successful achievement of the desired orientation. The rich contributions of electrochemistry, spectroscopy (especially infrared spectroscopy), modeling, and microscopy are featured, along with their limitations.

Micro‐ and Nanoscopic Imaging of Enzymatic Electrodes: A Review

“…We already described the contribution of microscopy to study enzyme orientation in a previous review . Therefore, we will here only briefly summarize the main articles.…”

“…Moreover, an effective electron coupling between the protein redox centers and the electrode is a key prerequisite to efficient devices. This latter point is not trivial due to the size of the molecules and their structural complexity . The enzyme activity relies on a redox active site mostly deeply buried in the enzyme dielectric structure, and sometimes accompanied by electronic relays that drive electrons between the active site and the surface of the molecule, which results in a huge anisotropy of enzyme electronic properties.…”

“…The enzyme activity relies on a redox active site mostly deeply buried in the enzyme dielectric structure, and sometimes accompanied by electronic relays that drive electrons between the active site and the surface of the molecule, which results in a huge anisotropy of enzyme electronic properties. The electronic communication between an enzyme and an electrode can be direct ( i. e . electrons tunnel directly from the enzyme active site or electron relays to the electrode or reciprocally) or indirect (the indirect electron transfer is also called “mediated electron transfer”) .…”

Implicit modeling of the impact of adsorption on solid surfaces for protein mechanics and activity with a coarse-grain representation

“…One of the main issues that are addressed when investigating protein/surface interaction, is the matter of protein orientation. Controlled adsorption with ordered proteins is essential for devices such as biosensors, where antibodies should be immobilized with a specific orientation favoring the following antibody-antigen binding (2), or for bioelectrocatalysis devices (biofuel cells or bioreactors for electrosynthesis), where a correct enzyme orientation is essential for direct electron transfer between the adsorbed protein and the electrode (3,4). The adsorbed proteins' orientation depends on many factors, such as their charge, size or shape, the support properties, or external conditions like the temperature and pH (5).…”

Enzyme Immobilization for Solid-Phase Catalysis

“…Enzymes are routinely leveraged to enable unique applications throughout research, industrial production and molecular diagnostics as they are known to accelerate reactions by >10 17 fold [1]. Enzyme immobilization has been an area of great interest since it was first reported in 1916 [2], with many reviews available [3][4][5][6][7][8][9][10][11]. Immobilization is achieved by anchoring enzymes to or within solid supports in order to facilitate efficient separation from the reaction media in heterogeneous systems and increase the reusability of enzymes.…”