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At least 847 records · Page 47Linked to original sources
PubMed1996

Effect of potential binding site overlap to binding of cellulase to cellulose: a two-dimensional simulation.

A computer simulation model for the binding of ligands to a totally anisotropic surface (infinite two-dimensional square lattice) with overlapping binding sites has been developed. The validity of the simulation has been proven by comparison with cases where the correct results are known. The simulation of kinetics shows that when the lattice is close to saturation, the true equilibrium state is reached extremely slowly due to a lot of rearranging of the ligands on the lattice. Based on these findings, the terms 'apparent saturation' and 'apparent maximum coverage' have been introduced and defined. The largest discrepancies between 'apparent maximum coverage' and the theoretically predicted value were observed for ligands of large size and/or irregular shape. As an example, the model has been applied to describe the binding of cellobiohydrolase-I core to Avicel. A formula for calculation of the intrinsic binding constant, maximal binding capacity and specific surface of cellulose from real binding data has been derived.

Adsorption↗
PubMed1981

Improved viscometric assay for cellulase.

A viscometric assay for the determination of carboxymethylcellulase activity is described. The method, which is developed from a direct theoretical approach, takes into account a kinetic energy correction and the non-Newtonian behaviour of carboxymethylcellulose solutions. The enzymic hydrolysis of carboxymethylcellulose shows strong competitive inhibition by the products of the reaction and a method is presented for estimating the initial velocity of such reactions. A direct chemical determination of reducing end groups was used to confirm the validity of this approach.

Carboxymethylcellulose Sodium↗
PubMed1987

The expression of Cellulomonas fimi cellulase genes in Brevibacterium lactofermentum.

The exoglucanase gene (cex) and the endoglucanase A gene (cenA) from Cellulomonas fimi were subcloned into the Escherichia coli/Brevibacterium lactofermentum shuttle vector pBK10. Both genes were expressed to five to ten times higher levels in B. lactofermentum than in E. coli, probably because these genes were expressed from C. fimi promoters. In B. lactofermentum virtually all of the enzyme activities were in the culture supernatant. This system will facilitate analysis of the expression of the C. fimi genes in and secretion of their products from a Gram-positive bacterium.

Brevibacterium↗
PubMed1990

Nucleotide sequence and deletion analysis of the cellulase-encoding gene celH of Clostridium thermocellum.

The complete nucleotide sequence of the celH gene of Clostridium thermocellum was determined. The open reading frame extended over 2.7-kb DNA fragment and encoded a 900-amino acid (aa) protein (Mr 102,301) which hydrolyzes carboxymethylcellulose, p-nitrophenyl-beta-D-cellobioside, methylumbelliferyl- beta-D-cellobioside, barley beta-glucan, and larchwood xylan. The N terminus showed a typical signal peptide, and a cleavage site after Ser44 was predicted. Two Pro-Thr-Ser-rich regions divided the protein into three approximately equal domains. The central 328-aa region was similar to the N-terminal part, carrying the active site, of C. thermocellum endoglucanase E (EGE; 30.2%). The C-terminal region ended with two conserved 24-aa stretches showing close similarity with those previously described in EGA, EGB, EGD, EGE, EGX, and xylanase from C. thermocellum. Deletions of celH removing up to 327 codons from the 5' end and up to 245 codons from the 3' end of the coding sequence did not affect enzyme activity, confirming that the central domain was indeed responsible for catalytic activity. Production of truncated EGH in Escherichia coli was increased up to 120-fold by fusing fragments containing the 3' portion of the gene with the start of lacZ' present in pTZ19R.

Amino Acid Sequence↗
PubMedDate not supplied

Nucleotide sequence of the cellulase gene celF of Clostridium thermocellum.

The nucleotide sequence of the celF gene of Clostridium thermocellum was determined. The open reading frame extended over 2217 bp. The encoded 739-aa polypeptide, CelF, with a Mw = 82,015, was an endoglucanase with activity against carboxymethylcellulose. The N terminus showed a typical signal peptide, and a cleavage site after Ala-27 was predicted. From residues 28 to 470, the sequence of CelF was related to the catalytic domains of type E2 endoglucanases, with a strong homology to the endoglucanases CelZ of Clostridium stercorarium and CenB of Cellulomonas fimi. The catalytic region was followed by a 134-aa segment also present in C. stercorarium CelZ and in C. fimi CenB, and belonging to the family of non-catalytic, presumably cellulose-binding domains first identified in Bacillus subtilis endoglucanase. A 21-aa segment rich in Pro/Thr/Ser residues separated the putative cellulose-binding region from the COOH-terminal region, which contained two conserved stretches of 24 amino acids closely similar to those previously described in endoglucanases CelA, CelB, CelD, CelE, CelH and CelX, and xylanase XynZ of C. thermocellum.

Bacillus subtilis↗
PubMed2005

Structure of a full length psychrophilic cellulase from Pseudoalteromonas haloplanktis revealed by X-ray diffraction and small angle X-ray scattering.

Pseudoalteromonas haloplanktis is a psychrophilic Gram-negative bacterium isolated in Antarctica, that lives on organic remains of algae. This bacterium converts the cellulose, highly constitutive of algae, into an immediate nutritive form by biodegrading this biopolymer. To understand the mechanisms of cold adaptation of its enzymatic components, we studied the structural properties of an endoglucanase, Cel5G, by complementary methods, X-ray crystallography and small angle X-ray scattering. Using X-ray crystallography, we determined the structure of the catalytic core module of this family 5 endoglucanase, at 1.4A resolution in its native form and at 1.6A in the cellobiose-bound form. The catalytic module of Cel5G presents the (beta/alpha)(8)-barrel structure typical of clan GH-A of glycoside hydrolase families. The structural comparison of the catalytic core of Cel5G with the mesophilic catalytic core of Cel5A from Erwinia chrysanthemi revealed modifications at the atomic level leading to higher flexibility and thermolability, which might account for the higher activity of Cel5G at low temperatures. Using small angle X-ray scattering we further explored the structure at the entire enzyme level. We analyzed the dimensions, shape, and conformation of Cel5G full length in solution and especially of the linker between the catalytic module and the cellulose-binding module. The results showed that the linker is unstructured, and unusually long and flexible, a peculiarity that distinguishes it from its mesophilic counterpart. Loops formed at the base by disulfide bridges presumably add constraints to stabilize the most extended conformations. These results suggest that the linker plays a major role in cold adaptation of this psychrophilic enzyme, allowing steric optimization of substrate accessibility.

Amino Acid Sequence↗