Carbohydrate-Binding Modules of Potential Resources: Occurrence in Nature, Function, and Application in Fiber Recognition and Treatment

Abstract

Great interests have recently been aroused in the independent associative domain of glycoside hydrolases that utilize insoluble polysaccharides-carbohydrate-binding module (CBM), which responds to binding while the catalytic domain reacts with the substrate. In this mini-review, we first provide a brief introduction on CBM and its subtypes including the classifications, potential sources, structures, and functions. Afterward, the applications of CBMs in substrate recognition based on different types of CBMs have been reviewed. Additionally, the progress of CBMs in paper industry as a new type of environmentally friendly auxiliary agent for fiber treatment is summarized. At last, other applications of CBMs and the future outlook have prospected. Due to the specificity in substrate recognition and diversity in structures, CBM can be a prosperous and promising 'tool' for wood and fiber processing in the future.

Keywords: CBM conjugate additives; CBM-substrate interactions; carbohydrate-binding modules (CBM); classification and configuration.

Figure 2

Identification of fibers and substrates by different CBMs. (a) Strategies for site-specific and high-loading GFP immobilization on microcrystalline cellulose, reprinted from Ref [81] with permission from American Chemical Society. The GFP−scaffoldin complex could be immobilized on the cellulose surface via CBM−cellulose interaction; (b) Schematic representation of a cellulose nanocrystal(CNC) covered with CBM-PEG, reprinted from Ref [87] with permission from American Chemical Society; (c) Schematic illustration of morphogenesis of cellulose fibers mediated by CBM1: (i) CBM on the surface of cellulose; (ii) CBM-promoted amorphization, reprinted from Ref [89] with permission from Elsevier; (d) AFM studies different lignin coverage, lignin types of substrates, and the total adhesion of biomass to CBM as a function of surface lignin coverage, reprinted from Ref [95] with permission from American Chemical Society; (e) Confocal analysis of interactions between CBMs (labeled with Alexa Fluor 488 C5 Maleimide(Invitrogen)) and filter paper (FP) samples, reprinted from Ref [89] with permission from Elsevier.

Figure 1

Different types of CBM: (a) Type-A, CBM3; (b) Type-B, CBM4; (c) Type-C, CBM9; (d) Schematic of binding of type-A (left) and type-B (right) CBMs on nanocrystalline cellulose (CNC) reprinted from Ref [53] with permission from Elsevier; (e) Type-A CBM1 with SUMO solubilizing label. The above structure diagrams are drawn using the base sequences from Table 1 through the Swiss model and Pymol.

Figure 3

(a) A schematic presentation of the structure of the composite, reprinted from Ref [115] with permission from John Wiley and Sons. At the molecular level there are two functional blocks of the fusion protein amphiphilic hydrophobin−cellulose−binding domains (HFBI-DCBD) and its target surfaces; (b) Schematic structures of double CBMs, adapted from Ref [116]; (c) Shopper−Rieler Index of the E. globulus and P. sylvestris fibers treated with CBM, CBM-PEG and untreated, reprinted from Ref [67] with permission from Springer Nature; (d) (i) Impact of increasing refining energies on ease of enzyme−mediated hydrolysis of the microfibrillated cellulose (MFC) substrates. (ii) Impact of the refining energy on the fiber morphology. (iii) Impact of increasing refining energies on cellulose−binding module accessibility to the MFC substrates, reprinted from Ref [87] with permission from American Chemical Society; (e) SEM images of CF11 fibers treated with (i) and without (ii) CBD, reprinted from Ref [113] with permission from American Chemical Society.