## 1 Introduction  
The high demand for biofriendly energy and chemical sources has led to intensive studies on the processing of lignocellulosic biomass for commercial-scale application [1, 2, 3]. Found in all plants, lignocellulosic is responsible for the stable structure of the cell wall, consisting of a cellulose core structure, which is tightly wrapped in a meshwork of interlinked hemicellulose and lignin polymers [4]. Cellulose is a promising carbohydrate source for biofuel production, such as ethanol, fatty acids, or long-chain alkyls [5, 6], and other feedstocks such as gluconic acid [7] or sorbitol [8]. However, the degradation of natural cellulosic materials is challenging because cellulose is not only wrapped by the surrounding plant polymers but also forms stable crystalline microfibril structures by intra- and intermolecular hydrogen bonds between the cellulose polymer strands.  
In nature, certain microorganisms effectively digest cellulose utilizing a concert of multiple enzymes [9; 10; 11]. Glycoside hydrolases (GHs) are the major players in cellulose degradation, and at least three types of these are required to entirely metabolize cellulosic biomass into monomeric glucose: (I) endoglucanases (EGs) act on amorphous regions of cellulosic material to break glycoside bonds and produce a variety of oligosaccharides; (II) cellobiohydrolases (CBHs, also known as exoglucanases) digest polysaccharide strands progressively from the reducing (type I) or the non-reducing ends (type II) to generate cellobiose; and (III) \(\beta\)-glucosidase yields fermentatable monomeric glucose by hydrolyzing cellobiose [12].  
Artificial GH complexes have been studied [13], inspired by natural multienzyme complexes that efficiently hydrolyze crystalline cellulose. Cellulosomes, first discovered in _Acetivibrio thermocellus_ (formerly _Clostridium thermocellum_), are highly active cellulolytic multienzyme complexes displayed on the cell wall [14; 15; 16]. Environment-adapted lignocellulosic-degrading enzymes are co-expressed and loaded onto the central scaffold protein, scaffold, via interactions between their dockerin domains and the cohesion domains of scaffoldin [17]. Scaffoldin contains a carbohydrate-binding module (CBM) and facilitates the association of the catalytic modules, such as EGs and CBHs, with the substrate. The [PERSON] group has been conducting pioneering studies to build artificial cellulosomes using an engineered scaffold protein consisting of one CBM and distinct cohesion domains with enhanced cellulose degradation [15; 18]. Another group demonstrated that the functional components were assembled on a nano-scaffold using the biotin-streptavidin interaction [19; 20]. Furthermore, artificial cellulosomes in which cellulose-acting components were site-specifically assembled on DNA scaffolds have also been developed [21; 22].  
Cellulaes acting on crystalline substrates, whether or not they are cellulosomal enzymes, are usually multidomain proteins containing a single catalytic domain and CBM(s). CBMs play an important role in the processive hydrolysis of crystalline celluloses [23; 24]. Therefore, it is unclear whether the enhancement of hydrolysis by the assembly of multiple GHs is due to the assembly of different catalytic domains or to that of multiple CBMs. In this study, multiple GHs lacking CBMs were assembled in order to reveal the true effect of multiple conjoined GHs. Although no significant synergistic effect of catalytic domain clustering on the cellulose hydrolysis was observed, reversible assembly with CBM enhanced hydrolysis by the catalytic domains. This finding suggests that the reversible incorporation of a separate substrate-binding domain is a promising approach to effectively utilize enzymes that act on polymer substrates, other than cellulosic polymers.