Bacterial cellulases

Bacteria represent a promising source for the production of industrial enzymes. Bacterial cellulases are an especialfy interesting case in point. Many thermophilic bacterial species produce cellulases that are stable and active at high temperature, resistant to proteolytic attack, and stable to mechanical and chemical denaturation. However, cellulase productivities in bacteria are notoriously low compared to other microbial sources. In this paper bacterial enzyme production systems will be discussed with a focus on comparisons of the productivities of known bacterial cellulase producers. In an attempt to draw conclusions concerning the regulation of cellulase synthesis in bacterial systems, a tentative model for regulation in Acidothennus cellulofyticus has been developed. 

It is now apparent that many bacterial cellulases are composed of two or more structural and functional units or domains and it has been suggested that such enzymes arose by a process of domain shuffling (1). The domains may be catalytic or non-catalytic and their occurrence is often indicated in the primary protein structure by an intervening... 

These results demonstrate several useful properties of the C. fimi CBDs for enzyme immobilization and purification. Presumably, the CBDs of other bacterial cellulases (Figure 3) can be used in similar ways. It remains to be seen whether these differ significantly in their affinity or capacity for adsorption if so, certain CBDs may be preferable for specific purposes. 

Endocellulases have been isolated from plant pathogenic nematodes and four structural genes were cloned from two species [21]. AU of the ceUulase catalytic domains belong to family 5 and two of them also code for family II CBDs. The enzymes show 37 % identity in their amino acid sequence to several bacterial cellulases. 

Gilkes N, Jervis E, Henrissat B, Tekant B, Miller RC Jr, Warren RAJ, Kilburn DG (1992) The adsorption of a bacterial cellulase and its two isolated domains to crystalline cellulose. Journal of Biological Chemistry 267 6743 - 6749... 

Din N, Gilkes NR, Tekant B, Miller RC Jr, Warren RA, Kilburn DG (1991) Non-hydrolytic disruption of cellulose fibres by the binding domain of a bacterial cellulase. Bio/Technolog 9 1096-1099... 

Cellulase-producing bacteria include CelMomonas, Clostridium, Pseudomonas, Streptomyces, Thermonospora, and Ruminococcus, but bacterial cellulases digest cotton fibers to lower levels compared to amorphous celluloses (Ray et al., 2006). Cellulases have two functionally distinct domains in their structure, namely catalytic domain and cellulose substrate binding domain, linked by an interdomain, glycosylated linker peptide at either the N or the C terminal of the protein cellulose binding domains exhibit different affinities, specificities, some binding to crystalline cellulose, while others restrict themselves to the disordered regions. Catalytic domain has an active site in the shape of a tunnel or cleft where hydrolytic reactions take place (Cavedon et al., 1990 Lee et al., 1996). 

Enzymes acting on molecules like cellulose, which are insoluble and of similar, or even greater size than themselves, obviously require delicate tertiary structures comparison of the sequence of approximately 50 fungal and bacterial cellulase genes and of some other polysaccharide hydrolase (for review see [8]) has offered evidence that such proteins are composed of separate domains, which allow a spacial separation of the sites involved in substrate recognition and enzymatic activity. 

Bacterial cellulases have applications in agricultural and industrial processes, including laundry and detergents, textile, food and animal feed, pulp and paper, and biofuel industries... 

Din, N Gilkes, NR Tekant, B Miller, RC Jr. Warren, RAJ KUbum, DG. Non-Hydrolytic Dismption of Cellulose Fibres by the Binding Domain of a Bacterial Cellulase. Bio/Technology, 1991, 9,1096-9. 

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