Progress curves

Abstract

The chain-end preference and processivity of the cellulases 1,4-β-D-glucan-cellobiohydrolase I (CBH I) and 1,4-β-D-glucan-cellobiohydrolase II (CBH II) from Trichoderma reesei and 1,4-β-D-glucancellobiohydrolase 50 (CBH 50) and 1,4-β-D-glucan-cellobiohydrolase 58 (CBH 58) from Phanerochaete chrysosporium were studied by comparing experimental degradation data on reducing end-labelled bacterial microcrystalline cellulose with computer simulations of different models. Our results with T. reesei and P. chrysosporium cellulases show that there is a common pattern of hydrolysis for CBH-I-type enzymes and another clearly distinguishable pattern for CBH-II-type enzymes, especially in the initial part of the progress curve.Keywords : cellulase ; cellulose; hydrolysis ; simulation ; mode of action.In nature, the breakdown of cellulose is carried out mainly by fungi and bacteria. These organisms degrade crystalline cellulose by means of several enzymes acting at the ends (exocellulases) or randomly (endoglucanases) on the cellulose chains. Cellulases, like many other enzymes attacking insoluble or 'larger-than-enzyme' polymeric substrates, have a characteristic two-domain organisation : a catalytic domain connected by a flexible linker to a separate cellulose-binding domain [1]. Effective degradation of native cellulose requires cooperation between different functional types of cellulases and displays two distinctive modes of synergism; namely, cooperation among endoglucanases and cellobiohydrolases (CBHs) (endo/exo synergism), where the endoglucanases are supposed to create a large number of free ends susceptible to exoglucanase action [2Ϫ4], and cooperation among different CBHs [5Ϫ7]. The molecular basis for this latter synergism is not yet understood, mainly because the modes of action of the individual enzymes on crystalline cellulose are not known. By definition, CBHs attack the cellulose chain from the non-reducing end [8]. Recent data indicate, however, that the exhaustively studied Trichoderma reesei 1,4-β-D-glucan-cellobiohydrolase I (CBH I) preferentially attacks the reducing end of cellooligosaccharides, whereas the similarly well-characterised 1,4-β-D-glucan-cellobiohydrolase II (CBH II) from the same organism indeed prefers the non-reducing end [9,10].

Purification and Characterization of Cellulase from Termite Ametermes eveuncifer (Silverstri) Soldiers

“…It is used in plants and agricultural waste processing (Mswaka & Magan, 1998;Lu et al, 2004), biofuels (Vaithanomsat et al, 2009), triphase biomethanation (Chakraborty et al, 2000), chiral separation and ligand binding studies (Nutt et al, 1998). An in-depth study of the enzymes involved in the degradation of cellulose and other polysaccharides in termites will play a key role towards discovering novel approaches in termite control, removal of cellulosic waste, improved knowledge of polysaccharide degradation which might drive the discovery of novel industrial enzymes as well as industrial methods in alternative fuel generation from cellulosic materials.…”

Two new cellulosome components encoded downstream of celI in the genome of Clostridium thermocellum: the non-processive endoglucanase CelN and the possibly structural protein CseP

“…These carbohydrate-binding modules (CBMs) have a stimulating effect by increasing enzyme-substrate proximity, helping the enzyme to overcome the liquid-solid interface and enhancing the accessibility of the substrate surface by interacting with the crystal (Bolam et al, 1998;Nutt et al, 1998;Pagès et al, 1997). They are indispensable in catalytic systems where the size relationship between substrate and enzyme(s) seriously limits the molecular dynamics of enzyme action.…”

A newly described cellulosomal cellobiohydrolase, CelO, from Clostridium thermocellum: investigation of the exo-mode of hydrolysis, and binding capacity to crystalline cellulose The GenBank accession number for the sequence determined in this work is AJ275975.

“…These carbohydrate-binding modules (CBMs) have a stimulating effect by increasing enzyme-substrate proximity (Bolam et al, 1998) ; they help the enzyme to overcome the liquid-solid interface (Nutt et al, 1998) and also enhance the accessibility of the substrate surface by modifying the structure of the cellulose crystal (Page' s et al, 1997). On the basis of sequence comparison, 26 families of substrate-binding modules from bacteria, with between 40 and 180 amino acids, have been defined (Coutinho & Henrissat, http :\\afmb.cnrs-mrs.fr\ "pedro\DB\db.html ;Tomme et al, 1998).…”