Dataset Information

The fibronectin type 3-like repeat from the Clostridium thermocellum cellobiohydrolase CbhA promotes hydrolysis of cellulose by modifying its surface.

ABSTRACT: Fibronectin type 3 homology domains (Fn3) as found in the cellobiohydrolase CbhA of Clostridium thermocellum are common among bacterial extracellular glycohydrolases. The function of these domains is not clear. CbhA is modular and composed of an N-terminal family IV carbohydrate-binding domain (CBDIV), an immunoglobulin-like domain, a family 9 glycosyl hydrolase catalytic domain (Gh9), two Fn3-like domains (Fn3(1,2)), a family III carbohydrate-binding domain (CBDIII), and a dockerin domain. Efficiency of cellulose hydrolysis by truncated forms of CbhA increased in the following order: Gh9 (lowest efficiency), Gh9-Fn3(1,2) (more efficient), and Gh9-Fn3(1,2)-CBDIII (greatest efficiency). Thermostability of the above constructs decreased in the following order: Gh9 (most stable), Gh9-Fn3(1,2), and then Gh9-Fn3(1,2)-CBDIII (least stable). Mixing of Orpinomyces endoglucanase CelE with Fn3(1,2,) or Fn3(1,2)-CBDIII increased efficiency of hydrolysis of acid-swollen cellulose (ASC) and filter paper. Scanning electron microscopic studies of filter paper treated with Fn3(1,2), Fn3(1,2)-CBDIII, or CBDIII showed that the surface of the cellulose fibers had been loosened up and crenellated by Fn3(1,2) and Fn3(1,2)-CBDIII and to a lesser extent by CBDIII. X-ray diffraction analysis did not reveal changes in the crystallinity of the filter paper. CBDIII bound to ASC and filter paper with capacities of 2.45 and 0.73 micro moles g(-1) and relative affinities (K(r)) of 1.12 and 2.13 liters g(-1), respectively. Fn3(1,2) bound weakly to both celluloses. Fn3(1,2)-CBD bound to ASC and filter paper with capacities of 3.22 and 0.81 micro moles g(-1) and K(r)s of 1.14 and 1.98 liters g(-1), respectively. Fn3(1,2) and CBDIII contained 2 and 1 mol of calcium per mol, respectively. The results suggest that Fn3(1,2) aids the hydrolysis of cellulose by modifying its surface. This effect is enhanced by the presence of CBDIII, which increases the concentration of Fn3(1,2) on the cellulose surface.

SUBMITTER: Kataeva IA

PROVIDER: S-EPMC124122 | biostudies-literature | 2002 Sep

REPOSITORIES: biostudies-literature

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The fibronectin type 3-like repeat from the Clostridium thermocellum cellobiohydrolase CbhA promotes hydrolysis of cellulose by modifying its surface.

Kataeva Irina A IA Seidel Ronald D RD Shah Ashit A West Larry T LT Li Xin-Liang XL Ljungdahl Lars G LG

Applied and environmental microbiology 20020901 9

Fibronectin type 3 homology domains (Fn3) as found in the cellobiohydrolase CbhA of Clostridium thermocellum are common among bacterial extracellular glycohydrolases. The function of these domains is not clear. CbhA is modular and composed of an N-terminal family IV carbohydrate-binding domain (CBDIV), an immunoglobulin-like domain, a family 9 glycosyl hydrolase catalytic domain (Gh9), two Fn3-like domains (Fn3(1,2)), a family III carbohydrate-binding domain (CBDIII), and a dockerin domain. Effi ...[more]

PMID: 12200278

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Project description:BackgroundClostridium thermocellum is a thermophilic anaerobic bacterium that degrades cellulose by using a highly effective cellulosome, a macromolecular complex consisting of multiple cellulose degrading enzymes organized and attached to the cell surface by non-catalytic scaffoldins. However, due largely to lack of efficient methods for genetic manipulation of C. thermocellum, it is still unclear how the different scaffoldins and their functional modules contribute to cellulose hydrolysis.ResultsWe constructed C. thermocellum mutants with the primary scaffoldin CipA (cellulosome-integrating protein A) truncated at different positions or lacking four different secondary scaffoldins by using a newly developed thermotargetron system, and we analyzed cellulose hydrolysis, cellulosome formation, and cellulose binding of the mutants. A CipA truncation that deletes six type I cohesin modules, which bind cellulolytic enzymes, decreased cellulose hydrolysis rates by 46%, and slightly longer truncations that also delete the carbohydrate binding module decreased rates by 89 to 92%, indicating strong cellulosome-substrate synergy. By contrast, a small CipA truncation that deletes only the C-terminal type II dockerin (XDocII) module detached cellulosomes from the cells, but decreased cellulose hydrolysis rates by only 9%, suggesting a relatively small contribution of cellulosome-cell synergy. Disruptants lacking any of four different secondary scaffoldins (OlpB, 7CohII, Orf2p, or SdbA) showed moderately decreased cellulose hydrolysis rates, suggesting additive contributions. Surprisingly, the CipA-ΔXDocII mutant, which lacks cell-associated polycellulosomes, adheres to cellulose almost as strongly as wild-type cells, revealing an alternate, previously unknown cellulose-binding mechanism.ConclusionsOur results emphasize the important role of cellulosome-substrate synergy in cellulose degradation, demonstrate a contribution of secondary scaffoldins, and suggest a previously unknown, non-cellulosomal system for binding insoluble cellulose. Our findings provide new insights into cellulosome function and impact genetic engineering of microorganisms to enhance bioconversions of cellulose substrates.

Project description:Background: The ability of Clostridium thermocellum ATCC 27405 wild-type strain to hydrolyze cellulose and ferment the degradation products directly to ethanol and other metabolic byproducts makes it an attractive candidate for consolidated bioprocessing of cellulosic biomass to biofuels. In this study, whole-genome microarrays were used to investigate the expression of C. thermocellum mRNA during growth on crystalline cellulose in controlled replicate batch fermentations. Results: A time-series analysis of gene expression revealed changes in transcript levels of ~40% of genes (~1300 out of 3198 ORFs encoded in the genome) during transition from early-exponential to late-stationary phase. K-means clustering of genes with statistically significant changes in transcript levels identified six distinct clusters of temporal expression. Broadly, genes involved in energy production, translation, glycolysis and amino acid, nucleotide and coenzyme metabolism displayed a decreasing trend in gene expression as cells entered stationary phase. In comparison, genes involved in cell structure and motility, chemotaxis, signal transduction and transcription showed an increasing trend in gene expression. Hierarchical clustering of cellulosome-related genes highlighted temporal changes in composition of this multi-enzyme complex during batch growth on crystalline cellulose, with increased expression of several genes encoding hydrolytic enzymes involved in degradation of non-cellulosic substrates in stationary phase. Conclusions: Overall, the results suggest that under low substrate availability, growth slows due to decreased metabolic potential and C. thermocellum alters its gene expression to (i) modulate the composition of cellulosomes that are released into the environment with an increased proportion of enzymes than can efficiently degrade plant polysaccharides other than cellulose, (ii) enhance signal transduction and chemotaxis mechanisms perhaps to sense the oligo-saccharide hydrolysis products, and nutrient gradients generated through the action of cell-free cellulosomes and, (iii) increase cellular motility for potentially orienting the cells’ movement towards positive environmental signals leading to nutrient sources. Such a coordinated cellular strategy would increase its chances of survival in natural ecosystems where feast and famine conditions are frequently encountered.

Project description:BackgroundThe ability of Clostridium thermocellum ATCC 27405 wild-type strain to hydrolyze cellulose and ferment the degradation products directly to ethanol and other metabolic byproducts makes it an attractive candidate for consolidated bioprocessing of cellulosic biomass to biofuels. In this study, whole-genome microarrays were used to investigate the expression of C. thermocellum mRNA during growth on crystalline cellulose in controlled replicate batch fermentations.ResultsA time-series analysis of gene expression revealed changes in transcript levels of ~40% of genes (~1300 out of 3198 ORFs encoded in the genome) during transition from early-exponential to late-stationary phase. K-means clustering of genes with statistically significant changes in transcript levels identified six distinct clusters of temporal expression. Broadly, genes involved in energy production, translation, glycolysis and amino acid, nucleotide and coenzyme metabolism displayed a decreasing trend in gene expression as cells entered stationary phase. In comparison, genes involved in cell structure and motility, chemotaxis, signal transduction and transcription showed an increasing trend in gene expression. Hierarchical clustering of cellulosome-related genes highlighted temporal changes in composition of this multi-enzyme complex during batch growth on crystalline cellulose, with increased expression of several genes encoding hydrolytic enzymes involved in degradation of non-cellulosic substrates in stationary phase.ConclusionsOverall, the results suggest that under low substrate availability, growth slows due to decreased metabolic potential and C. thermocellum alters its gene expression to (i) modulate the composition of cellulosomes that are released into the environment with an increased proportion of enzymes than can efficiently degrade plant polysaccharides other than cellulose, (ii) enhance signal transduction and chemotaxis mechanisms perhaps to sense the oligosaccharide hydrolysis products, and nutrient gradients generated through the action of cell-free cellulosomes and, (iii) increase cellular motility for potentially orienting the cells' movement towards positive environmental signals leading to nutrient sources. Such a coordinated cellular strategy would increase its chances of survival in natural ecosystems where feast and famine conditions are frequently encountered.

Dataset Information

The fibronectin type 3-like repeat from the Clostridium thermocellum cellobiohydrolase CbhA promotes hydrolysis of cellulose by modifying its surface.

Publications

The fibronectin type 3-like repeat from the Clostridium thermocellum cellobiohydrolase CbhA promotes hydrolysis of cellulose by modifying its surface.

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