Design of nanoscale enzyme complexes based on various scaffolding materials for biomass conversion and immobilization

Abstract

The utilization of scaffolds for enzyme immobilization involves advanced bionanotechnology applications in biorefinery fields, which can be achieved by optimizing the function of various enzymes. This review presents various current scaffolding techniques based on proteins, microbes and nanomaterials for enzyme immobilization, as well as the impact of these techniques on the biorefinery of lignocellulosic materials. Among them, architectural scaffolds have applied to useful strategies for protein engineering to improve the performance of immobilized enzymes in several industrial and research fields. In complexed enzyme systems that have critical roles in carbon metabolism, scaffolding proteins assemble different proteins in relatively durable configurations and facilitate collaborative protein interactions and functions. Additionally, a microbial strain, combined with designer enzyme complexes, can be applied to the immobilizing scaffold because the in vivo immobilizing technique has several benefits in enzymatic reaction systems related to both synthetic biology and metabolic engineering. Furthermore, with the advent of nanotechnology, nanomaterials possessing ideal physicochemical characteristics, such as mass transfer resistance, specific surface area and efficient enzyme loading, can be applied as novel and interesting scaffolds for enzyme immobilization. Intelligent application of various scaffolds to couple with nanoscale engineering tools and metabolic engineering technology may offer particular benefits in research.

Keywords: Cell surface anchoring; Designer enzyme; Nanoparticle; Scaffold; Whole-cell biocatalyst.

Figure 1

Diagram illustrates the background of renewable biomass utilization and biorefineries using enzyme complexes. The enzyme complex is composed of hydrolysis enzymes and various types of scaffolds such as protein scaffolds, microbial scaffolds and nanomaterial scaffolds. The scaffold‐assembled enzymes have a high level of hydrolysis activity and can convert the various biomasses to valuable biomaterials.

Figure 2

The Diagram illustrates the structural organization of the plant cell wall. Enzymatic degradation of cellulose is protected by hemicelluloses and lignin. (A) Simple chemical composition of cellulose as glucose polymer and three types of cellulases for its enzymatic degradation. (B) Various components of hemicellulose with xylose backbone and multiple sets enzymes for its enzymatic hydrolysis.

Figure 3

Schematic illustrations of protein scaffolds based on the cellulosome system. (A) Native protein scaffold CbpA and CipA from C. cellulovorans and C. thermocellum, respectively. Dockerin‐cohesin interactions from different Clostridia strains have interspecies specificity. Thus, the cohesin modules in each strain were able to discriminate the dockerins in other strains. (B) Small recombinant protein scaffolds, miniCbpA and miniCipA, derived from native protein scaffolds CbpA and CipA, respectively. In addition, chimeric protein scaffolds combined with various cohesin modules from different Clostridia strains. Because the native protein scaffold is too large for expression by industrial microbe hosts, scaffoldin was spliced into a small recombinant protein scaffolds.

Figure 4

Schematic illustrations of advanced application of the microbial scaffold as surface display tool in bionanotechnology. Surface display based on anchoring modules for in vivo and in vitro immobilizations is shown as a diagram. The replacement of anchoring domains in protein scaffolds also leads to immobilization of enzymes on cell surface.

Figure 5

Four main methodologies for linking enzymes to nanoparticles, including (A) electrostatic adsorption, (B) covalent attachment to functionalized nanoparticles, (C) conjugation using proteins with a specific affinity, and (D) direct conjugation to the nanoparticle surface.