Do Cellulose Binding Domains Increase Substrate Accessibility?

Abstract

This article provides an overview of various theories proposed during the past five decades to describe the enzymatic hydrolysis of cellulose highlighting the major shifts that these theories have undergone. It also describes the effect of the cellulose-binding domain (CBD) of an exoglucanase/xylanase from bacterium Cellulomonas fimi on the enzymatic hydrolysis of Avicel. Pretreatment of Avicel with CBDCex at 4 and 37 degrees C as well as simultaneous addition of CBDCex to the hydrolytic enzyme (Celluclast, Novo, Nordisk) reduced the initial rate of hydrolysis owing to irreversible binding of CBD proteins to the substrate's binding sites. Nonetheless, near complete hydrolysis was achieved even in the presence of CBDCex. Protease treatment of both pure and CBDCex-treated Avicel reduced the substrates' hydrolyzability, perhaps owing to proteolysis of the hydrolyzing enzyme (Celluclast) by the residual Proteinase K remaining in the substrate. Better protocols for complete removal of CBD proteins from the substrate need to be developed to investigate the effect of CBD adsorption on cellulose digestibility.

Synergistic interactions in cellulose hydrolysis

“…Wood and McCrae, on the other hand, argued that the C 1 component is composed of exocellulases and that the initial attack on the sub strate is carried out by the endocellulases in the C x com ponent. In their endo-exo model, the C x component carries out the function proposed by Reese [63], some researchers proposed that the CBM may carry out the role of disrupting the substrate, making it more accessible for the CD [64][65][66]. While a number of studies have demonstrated some cellulose disrupting ability by various CBMs from native cellu lases, their ability to synergize with CDs appears to be weak at best [10,66].…”

Characterization and aging of biotreated kraft bagasse pulp

“…Lignocellulosic materials, biopulping, biobleaching, and pulp modifications represent biotechnical applications with the greatest potential in terms of cost reduction, energy consumption, process improvement paper quality, and decrease in environmental impacts. 3 There have been only a few studies on wood treatment with bacteria as compared to fungi. 4,5 The potential advantages of using bacteria instead of fungi are possibly shorter treatment times due to higher growth rates, more convenient inoculation, and more economic inoculum preparation techniques.…”

Recent developments on cellulases and carbohydrate-binding modules with cellulose affinity

“…However, another CBM1, this time from Trichoderma reesei endoglucanase Cel5A (in the article, using old terminology, unfortunately named EGIII instead of EGII or, preferably, Cel5A) was also suggested to have the same mode of action (Xiao et al 2001). Work with CBM2 from Cellulomonas fimi Xyn10A, actually contradicted the previous hypothesis that CBMs (at least of family 2) could change the digestibility of the enzyme substrate (Esteghlalian et al 2001). Thus, the question still remains unanswered.…”