Polystyrene macroporous bead support for mammalian cell culture.
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Animals↗
Biomedical subjects
D G Kilburn
Publications and source records attributed to D G Kilburn.
Stereoselective hydrolysis catalyzed by related beta-1,4-glucanases and beta-1,4-xylanases.
Over 80 beta-1,4-glucanases and beta-1,4-xylanases can be classified into one of eight families on the basis of amino acid sequence similarities in their catalytic domains (Gilkes, N. R., Henrissat, B., Kilburn, D. G., Miller, R. C., Jr., and Warren, R. A. J. (1991) Microbiol. Rev. 55, 303-315). As a test of this classification, the stereochemical course of hydrolysis of 10 enzymes representative of five families has been determined using proton NMR. These data, together with published data for six additional enzymes, show that representatives of a given enzyme family have the same stereoselectivity: four families catalyze hydrolysis with retention of anomeric configuration, two with inversion. The results support the hypothesis that family members share a common general fold, active site topology, and catalytic mechanism.
Endo-1,4-beta Xylanases↗
Endoglucanase A from Cellulomonas fimi in which the hinge sequence of human IgA1 is substituted for the linker connecting its two domains is hydrolyzed by IgA proteases from Neisseria gonorrhoeae.
The hinge in IgA1 and the linker in endoglucanase A (CenA) are quite similar. The IgA1 hinge is 18 amino acids long and contains only proline, threonine and serine. The linker in CenA is 27 amino acids long and contains only proline, threonine and a single serine. IgA proteases from Neisseria gonorrhoeae cleave Pro-Ser and Pro-Thr bonds within the IgA1 hinge sequence, but they do not attack CenA. When the linker sequence of CenA is replaced with the hinge sequence of IgA1, the hybrid polypeptide is susceptible to the N. gonorrhoeae proteases. It is cleaved within the hinge sequence at the same sites as IgA1.
Amino Acid Sequence↗
The adsorption of a bacterial cellulase and its two isolated domains to crystalline cellulose.
CenA is a bacterial cellulase (beta-1,4-glucanase) comprised of a globular catalytic domain joined to an extended cellulose-binding domain (CBD) by a short linker peptide. The adsorption of CenA and its two isolated domains to crystalline cellulose was analyzed. CenA and CBD.PTCenA' (the CBD plus linker) adsorbed rapidly to cellulose at 30 degrees C, and no net desorption of protein was observed during the following 16.7 h. There was no detectable adsorption of the catalytic domain. Scatchard plots of adsorption data for CenA and for CBD.PTCenA were nonlinear (concave upward). The adsorption of CenA and CBD.PTCenA exceeded 7 and 8 mumol/g cellulose, respectively, but saturation was not attained at the highest total protein concentrations employed. A new model for adsorption was developed to describe the interaction of a large ligand (protein) with a lattice of overlapping potential binding sites (cellobiose residues). A relative equilibrium association constant (Kr) of 40.5 and 45.3 liter.g cellulose-1 was estimated for CenA and CBD.PTCenA, respectively, according to this model. A similar Kr value (33.3 liter.g-1) was also obtained for Cex, a Cellulomonas fimi enzyme which contains a related CBD but which hydrolyzes both beta 1,4-xylosidic and beta-1,4-glucosidic bonds. It was estimated that the CBD occupies approximately 39 cellobiose residues on the cellulose surface.
Adsorption↗
The tertiary structure of endo-beta-1,4-glucanase B (CenB), a multidomain cellulase from the bacterium Cellulomonas fimi.
Endo-beta-1,4-glucanase B (CenB) is a large (110 kDa) extracellular enzyme from the cellulolytic bacterium Cellulomonas fimi. CenB contains five domains, including a typical C.fimi cellulose-binding domain, separated by distinctive linker polypeptides (Meinke et al., 1991b). X-ray scattering analyses show that CenB has a highly elongated shape resembling beads on a string. The sizes of the polypeptides produced by treatment of CenB with proteases, together with their N-terminal amino acid sequences, show that at least two of the four linkers connecting the five domains of CenB are more sensitive to proteolysis than the domains themselves. It is concluded that the beads represent the domains of CenB, the string represents the linkers.
Actinomycetales↗
Cellulose-binding domains: potential for purification of complex proteins.
The endoglucanase CenA and the exoglucanase Cex from Cellulomonas fimi each contain a discrete cellulose-binding domain (CBD), at the amino-terminus or carboxyl-terminus respectively. The gene fragment encoding the CBD can be fused to the gene of a protein of interest. Using this approach hybrid proteins can be engineered which bind reversibly to cellulose and exhibit the biological activity of the protein partner. Alkaline phosphatase (PhoA) from Escherichia coli, and a beta-glucosidase (Abg) from an Agrobacterium sp. are dimeric proteins. The fusion polypeptides CenA-PhoA and Abg-CBC(Cex) are sensitive to proteolysis at the junctions between the fusion partners. Proteolysis results in a mixture of homo- and heterodimers; these bind to cellulose if one or both of the monomers carry a CBD, e.g. CenA-PhoA/CenA-PhoA and CenA-PhoA/PhoA. CBD fusion polypeptides could be used in this way to purify polypeptides which associate with the fusion partner.
Alkaline Phosphatase↗
The binding of Cellulomonas fimi endoglucanase C (CenC) to cellulose and Sephadex is mediated by the N-terminal repeats.
Endoglucanase C (CenC) from Cellulomonas fimi binds to cellulose and to Sephadex. The enzyme has two contiguous 150-amino-acid repeats (N1 and N2) at its N-terminus and two unrelated contiguous 100-amino-acid repeats (C1 and C2) at its C-terminus. Polypeptides corresponding to N1, N1N2, C1, and C1C2 were produced by expression of appropriate cenC gene fragments in Escherichia coli. N1N2, but not N1 alone, binds to Sephadex; both polypeptides bind to Avicel, (a heterogeneous cellulose preparation containing both crystalline and non-crystalline components). Neither C1 nor C1C2 binds to Avicel or Sephadex. N1N2 and N1 bind to regenerated ('amorphous') cellulose but not to bacterial crystalline cellulose; the cellulose-binding domain of C. fimi exoglucanase Cex binds to both of these forms of cellulose. Amino acid sequence comparison reveals that N1 and N2 are distantly related to the cellulose-binding domains of Cex and C. fimi endoglucanases A and B.
Actinomycetales↗
Structural and functional relationships in two families of beta-1,4-glycanases.
CenA and Cex are beta-1,4-glycanases produced by the cellulolytic bacterium Cellulomonas fimi. Both enzymes are composed of two domains and contain six Cys residues. Two disulfide bonds were assigned in both enzymes by peptide analysis of the isolated catalytic domains. A further disulfide bond was deduced in both cellulose-binding domains from the absence of free thiols under denaturing conditions. Corresponding Cys residues are conserved in eight of nine other known C. fimi-type cellulose-binding domains. CenA and Cex belong to families B and F, respectively, in the classification of beta-1,4-glucanases and beta-1,4-xylanases based on similarities in catalytic domain primary structure. Disulfide bonds in the CenA catalytic domain correspond to the two disulfide bonds in the catalytic domain of Trichoderma reesei cellobiohydrolase II (family B) which stabilize loops forming the active-site tunnel. Sequence alignment indicates the probable occurrence of disulfides at equivalent positions in the two other family B enzymes. Partial resequencing of the gene encoding Streptomyces KSM-9 beta-1,4-glucanase CasA (family B) revealed five errors in the original nucleotide sequence analysis. The corrected amino acid sequence contains an Asp residue corresponding to the proposed proton donor in hydrolysis catalysed by cellobiohydrolase II. Cys residues which form disulfide bonds in the Cex catalytic domain are conserved in XynZ of Clostridium thermocellum and Xyn of Cryptococcus albidus but not in the other eight known family F enzymes. Like other members of its family, Cex catalyses xylan hydrolysis. The catalytic efficiency (kcat/Km) for hydrolysis of the heterosidic bond of p-nitrophenyl-beta-D-xylobioside is 14,385 min-1.mM-1 at 25 degrees C; the corresponding kcat/Km for p-nitrophenyl-beta-D-cellobioside hydrolysis is 296 min-1.mM-1.
Actinomycetales↗
Glutamic acid 274 is the nucleophile in the active site of a "retaining" exoglucanase from Cellulomonas fimi.
In addition to its known substrate activity with p-nitrophenyl beta-cellobioside, the exoglucanase from Cellulomonas fimi has been shown to utilize substituted phenyl beta-glucosides as substrates, of which the best is 2',4'-dinitrophenyl beta-D-glucopyranoside. The enzyme can be inactivated by treatment with 2',4'-dinitrophenyl 2-deoxy-2-fluoro-beta-D-glucopyranoside, by trapping of the covalent intermediate in catalysis, as has been shown for a beta-glucosidase (Withers, S.G., and Street, I.P. (1988) J. Am. Chem. Soc. 110, 8551-8553). The intermediate formed is stable but can undergo turnover in the presence of cellobiose, reactivating the enzyme by transglycosylation. Using a tritium-labeled inactivator it has been possible to isolate and sequence a radiolabeled peptide from this enzyme, and the active site nucleophile has been identified as glutamic acid residue 274. This glutamic acid residue and its sequentially proximal amino acids are absolutely conserved in the homologous family F of cellulases.
Actinomycetales↗
Deletion of the linker connecting the catalytic and cellulose-binding domains of endoglucanase A (CenA) of Cellulomonas fimi alters its conformation and catalytic activity.
The Pro-Thr box is a linker of 23 amino acids ((PT)4T(PT)7) connecting the catalytic domain and the cellulose-binding domain (CBD) of endoglucanase A (CenA) from the bacterium Cellulomonas fimi. Deletion of the Pro-Thr box alters the conformation of CenA by changing the relative orientation of the catalytic domain and the CBD. The tertiary structures of the catalytic domain and the CBD appear to be unchanged. The change in conformation reduces the catalytic efficiency of the enzyme and masks one of two protease-sensitive sites between the domains. The deletion does not affect the adsorption of the enzyme to microcrystalline cellulose, but it does affect its desorption from cellulose. The results suggest that the Pro-Thr box in CenA has an extended, kinked, and rigid conformation.
Actinomycetales↗
High density cultivation of BSK cells on sintered alumina ceramic foam support.
A perfusion system which utilizes a porous ceramic core has been tested for the cultivation of transformed BHK cells which produce human transferrin. A design is presented in which cells are immobilized within the porous ceramic particle and are fed by continuous perfusion of batch liquid medium. It was found that more than 5 x 10(9) BHK cells could be supported within the 40 mL ceramic matrix, a ten-fold increase in cell density per unit surface area over the standard roller bottle cultures or a five-fold increase in volumetric cell density over suspension cultures. The cell specific productivity of human transferrin was similar to that observed in suspension culture. The system offer the advantages of significant reduction in serum requirements and the potential for scale-up.
Aluminum Oxide↗
Enzyme immobilization using a cellulose-binding domain: properties of a beta-glucosidase fusion protein.
Using molecular genetic techniques, a fusion protein has been produced which contains the cellulose-binding domain (CBD) of an exoglucanase (Cex) from Cellulomonas fimi fused to a beta-glucosidase (Abg) from Agrobacterium sp. The CBD functions as an affinity tag for the simultaneous purification and immobilization of the enzyme on cellulose. Binding to cellulose was stable for prolonged periods at temperatures from 4 degrees C to at least 50 degrees C, at ionic strengths from 10 mM to greater than 1 M, and at pH values below 8. The fusion protein can be desorbed from cellulose with distilled water or at pH greater than 8. Immobilized enzyme columns of the fusion protein bound to cotton fibers exhibited stable beta-glucosidase activity for at least 10 days of continuous operation at temperatures up to 37 degrees C. At higher temperatures, the bound enzyme lost activity. The thermal stability of the fusion protein was greatly improved by immobilization. Immobilization did not alter the pH stability. Except for its ability to bind to cellulose, the properties of the fusion protein were virtually the same as those of the native enzyme.
Adsorption↗
Nucleotide sequence of the endoglucanase C gene (cenC) of Cellulomonas fimi, its high-level expression in Escherichia coli, and characterization of its products.
The cenC gene of Cellulomonas fimi, encoding endoglucanase CenC, has an open reading frame of 1101 codons closely followed by a 9 bp inverted repeat. The predicted amino acid sequence of mature CenC, which is 1069 amino acids long, is very unusual in that it has a 150-amino-acid tandem repeat at the N-terminus and an unrelated 100-amino-acid tandem repeat at the C-terminus. CenC belongs to subfamily E1 of the beta-1,4-glycanases. High-level expression in Escherichia coli of cenC from a 3.6 kbp fragment of C. fimi DNA leads to levels of CenC which exceed 10% of total cell protein. Most of the CenC is in the cytoplasm in an inactive form. About 60% of the active fraction of CenC is in the periplasm. The catalytic properties of the active CenC are indistinguishable from those of native CenC from C. fimi. The Mr of CenC from E. coli and C. fimi is approximately 130 kDa. E. coli and C. fimi also produce an endoglucanase, CenC', of approximate Mr 120kDa and with the same N-terminal amino acid sequence and catalytic properties as CenC. CenC' appears to be a proteolytic product of CenC. CenC and CenC' can bind to cellulose and to Sephadex. CenC is the most active component of the C. fimi cellulase system isolated to date.
Amino Acid Sequence↗
Unusual sequence organization in CenB, an inverting endoglucanase from Cellulomonas fimi.
The nucleotide sequence of the cenB gene was determined and used to deduce the amino acid sequence of endoglucanase B (CenB) of Cellulomonas fimi. CenB comprises 1,012 amino acids and has a molecular weight of 105,905. The polypeptide is divided by so-called linker sequences rich in proline and hydroxyamino acids into five domains: a catalytic domain of 607 amino acids at the N terminus, followed by three repeats of 98 amino acids each which are greater than 60% identical, and a C-terminal domain of 101 amino acids which is 50% identical to the cellulose-binding domains of C. fimi cellulases Cex and CenA. A deletion mutant of the cenB gene encodes a polypeptide lacking the C-terminal 333 amino acids of CenB. The truncated polypeptide is catalytically active and, like intact CenB, binds to cellulose, suggesting that CenB has a second cellulose-binding site. The sequence of amino acids 1 to 461 of CenB is 35% identical, with a further 15% similarity, to that of a cellulase from avocado, which places CenB in cellulase family E. CenB releases mostly cellobiose and cellotetraose from cellohexaose. Like CenA, CenB hydrolyzes the beta-1,4-glucosidic bond with inversion of the anomeric configuration. The pH optimum for CenB is 8.5, and that for CenA is 7.5.
Amino Acid Sequence↗
Multiple domains in endoglucanase B (CenB) from Cellulomonas fimi: functions and relatedness to domains in other polypeptides.
Endoglucanase B (CenB) from the bacterium Cellulomonas fimi is divided into five discrete domains by linker sequences rich in proline and hydroxyamino acids (A. Meinke, C. Braun, N. R. Gilkes, D. G. Kilburn, R. C. Miller, Jr., and R. A. J. Warren, J. Bacteriol. 173:308-314, 1991). The catalytic domain of 608 amino acids is at the N terminus. The sequence of the first 477 amino acids in the catalytic domain is related to the sequences of cellulases in family E, which includes procaryotic and eucaryotic enzymes. The sequence of the last 131 amino acids of the catalytic domain is related to sequences present in a number of cellulases from different families. The catalytic domain alone can bind to cellulose, and this binding is mediated at least in part by the C-terminal 131 amino acids. Deletion of these 131 amino acids reduces but does not eliminate activity. The catalytic domain is followed by three domains which are repeats of a 98-amino-acid sequence. The repeats are approximately 50% identical to two repeats of 95 amino acids in a chitinase from Bacillus circulans which are related to fibronectin type III repeats (T. Watanabe, K. Suzuki, K. Oyanagi, K. Ohnishi, and H. Tanaka, J. Biol. Chem. 265:15659-15665, 1990). The C-terminal domain of 101 amino acids is related to sequences, present in a number of bacterial cellulases and xylanases from different families, which form cellulose-binding domains (CBDs). It functions as a CBD when fused to a heterologous polypeptide. Cells of Escherichia coli expressing the wild-type cenB gene accumulate both native CenB and a stable proteolytic fragment of 41 kDa comprising the three repeats and the C-terminal CBD. The 41-kDa polypeptide binds to cellulose but lacks enzymatic activity.
Amino Acid Sequence↗
Domains in microbial beta-1, 4-glycanases: sequence conservation, function, and enzyme families.
Several types of domain occur in beta-1, 4-glycanases. The best characterized of these are the catalytic domains and the cellulose-binding domains. The domains may be joined by linker sequences rich in proline or hydroxyamino acids or both. Some of the enzymes contain repeated sequences up to 150 amino acids in length. The enzymes can be grouped into families on the basis of sequence similarities between the catalytic domains. There are sequence similarities between the cellulose-binding domains, of which two types have been identified, and also between some domains of unknown function. The beta-1, 4-glycanases appear to have arisen by the shuffling of a relatively small number of progenitor sequences.
Amino Acid Sequence↗
Bacterial cellulose-binding domain-like sequences in eucaryotic polypeptides.
The catalytic domain of endoglucanase II of Trichoderma reesei and the spore germination-specific polypeptide 270-11 of Dictyostelium discoideum contain amino acid sequences which share identity with the sequences of the cellulose-binding domains of several bacterial beta-1,4-glycanases. This is the first report of the presence of such sequences in eucaryotic polypeptides.
Amino Acid Sequence↗
The tertiary structure of a bacterial cellulase determined by small-angle X-ray-scattering analysis.
CenA from Cellulomonas fimi is a beta-1,4-endoglucanase that binds tightly to cellulose. X-ray-scattering analyses show that the enzyme is tadpole-shaped: the previously identified catalytic and cellulose-binding domains comprise the head and tail respectively. It appears that this structural and functional organization is common to several cellulases from bacteria and fungi.
Actinomycetales↗