Cellulase Immobilization on Nanostructured Supports for Biomass Waste Processing

Abstract

Nanobiocatalysts, i.e., enzymes immobilized on nanostructured supports, received considerable attention because they are potential remedies to overcome shortcomings of traditional biocatalysts, such as low efficiency of mass transfer, instability during catalytic reactions, and possible deactivation. In this short review, we will analyze major aspects of immobilization of cellulase-an enzyme for cellulosic biomass waste processing-on nanostructured supports. Such supports provide high surface areas, increased enzyme loading, and a beneficial environment to enhance cellulase performance and its stability, leading to nanobiocatalysts for obtaining biofuels and value-added chemicals. Here, we will discuss such nanostructured supports as carbon nanotubes, polymer nanoparticles (NPs), nanohydrogels, nanofibers, silica NPs, hierarchical porous materials, magnetic NPs and their nanohybrids, based on publications of the last five years. The use of magnetic NPs is especially favorable due to easy separation and the nanobiocatalyst recovery for a repeated use. This review will discuss methods for cellulase immobilization, morphology of nanostructured supports, multienzyme systems as well as factors influencing the enzyme activity to achieve the highest conversion of cellulosic biowaste into fermentable sugars. We believe this review will allow for an enhanced understanding of such nanobiocatalysts and processes, allowing for the best solutions to major problems of sustainable biorefinery.

Keywords: biomass; cellulase; immobilization; nanostructured supports.

Scheme 1

Schematic representation of the review structure.

Figure 1

Functional modification of ZIF-8 (surface group modification/surface charge regulation) and its influence on immobilized cellulase (protects the spatial structure of proteins). Reproduced with permission from [45], Elsevier, 2021.

Figure 2

Formation of Zn-containing MOFs with encapsulated cellulase.

Figure 3

Hybrid cellulase-hydrogel nanobiocatalyst based on PANI nanorods formed on electrospun cationic poly(ε-caprolactone). Reproduced with permission from [72], Elsevier, 2022.

Figure 4

Schematic of the formation mechanism of ECG-NFs and the functional mechanism of cellulase. Reproduced with permission from [79], American Chemical Society, 2021.

Figure 5

Schematic representation of the biomass waste hydrolysis to glucose with the nanobiocatalyst containing two enzymes adsorbed on sophisticated porous silica NPs. Reproduced with permission from [27], American Chemical Society, 2022.

Figure 6

Schematic illustration of (A) the structural organization of the cellulosome of Clostridium thermocellum, (B) Ni-NTA-functionalized micelles for immobilizing cellulases, and (C) the interaction of Ni-NTA with His₆-tagged cellulases. Reproduced with permission from [89], Wiley, 2019.

Figure 7

(a) Cartoon illustrating the three types of magnetic micromotors using poly(L-lysine) (PLL), cellulase, and PEG as terminating layer, resulting in ^xM_M-PLL, ^xM_M-C, and ^xM_M-PEG, respectively (x indicates the motor size). (b) The locomotion of the micromotors was assessed in water filled microchannels and in structured paper chips. The movement of the micromotors was induced due to the exposure to magnets with different magnetic forces. Reproduced with permission from [118], Royal Society of Chemistry, 2021.

Figure 8

Representative illustration for immobilizing cellulase enzyme on to halloysite nanotubes as a template/matrix using aminosilane as a cross-linker. Prior to this, iron oxide nanoparticles were synthesized over halloysite nanotubes concurrent with their deposition, rendering the nanobiocatalyst recoverable using a magnet. Reproduced with permission from [120], American Chemical Society, 2020.

Figure 9

Schematic representation of the immobilization of three enzymes on amino-functionalized magnetite NPs and hydrolysis of sugarcane bagasse pulp. TEOS and APTES stand for tetraethoxysilane and (3-aminopropyl) triethoxysilane, respectively. Reproduced with permission from [138], American Chemical Society, 2018.

Figure 10

Schematic representation of the recyclable Eud-IDA-Ni²⁺/EG5C-1 biocomposite which is soluble at pH above 5.5 and insoluble for separation at pH below 4.5, can effectively hydrolyze cellulose. Reproduced with permission from [141], American Chemical Society, 2021.