Deduced amino acid sequence and possible catalytic residues of a thermostable, alkaline cellulase from an Alkaliphilic bacillus strain

Alkaliphilic Bacillus sp. strain KSM-S237 (a relative of Bacillus pseudofirmus) produces a thermostable, alkaline endo-1,4-beta-glucanase (Egl). The entire gene for the enzyme harbored a 2,472-bp open reading frame (ORF) encoding 824 amino acids, including a 30-aminoacid signal peptide. The deduced amino acid sequence of the mature enzyme (794 amino acids, 88,284 Da) showed very high similarity to those of family 5 mesophilic, alkaline Egls from some alkaliphilic bacilli. The enzyme had a region similar to a novel cellulose binding domain proposed for an Egl (EngF) from Clostridium cellulovorans. Expression of the Bacillus Egl gene in Bacillus subtilis resulted in high carboxymethy cellulase activity (2.0 g/l) in the culture broth, concomitant with the appearance of a protein band on an SDS gel at 86 kDa. Site-directed mutagenesis delineated the importance of Arg111, His151, Glu190, His262, Tyr264, and Glu305 in catalysis and/or substrate binding of the enzyme.     

A novel alkaline endoglucanase from an alkaliphilic Bacillus isolate: enzymatic properties, and nucleotide and deduced amino acid sequences

A highly alkaline endo-1,4-beta-glucanase (Egl) was purified to homogeneity from a culture broth of alkaliphilic Bacillus sp. strain KSM-N252. The optimal pH for activity was as high as 10, and the optimal temperature was 55 degrees C. The molecular mass and isoelectric point were around 50 kDa and pH 4.2, respectively. The enzyme hydrolyzed carboxymethyl cellulose in a random fashion. Unlike previously reported Egls, the enzyme was highly active on p-nitrophenyl cello-oligosaccharides and acid-swollen cellulose, and its activity was stimulated by cellobiose at high concentrations. The entire gene for the enzyme contained a 1,476-bp single open reading frame encoding 492 amino acids, including a 29-amino-acid signal peptide. The mature enzyme (463 amino acids: 51,174 Da) exhibited moderate homology to other family 5 alkaline Egls. In the C-terminal region, a carbohydrate-binding module that belongs to family XII was repeated. Furthermore, four and six repeats of Pro-Pro-Ser/Thr-Glu/Asp-Pro-(Glu) were found immediately before the first and second carbohydrate-binding modules, respectively.     

Cloning of an endoglycanase gene from Paenibacillus cookii and characterization of the recombinant enzyme

An endoglycanase gene of Paenibacillus cookii SS-24 was cloned and sequenced. This Pgl8A gene had an open reading frame of 1,230 bp that encoded a putative signal sequence (31 amino acids) and mature enzyme (378 amino acids: 41,835 Da). The enzyme was most homologous to a β-1,3-1,4-glucanase of Bacillus circulans WL-12 with 84% identity. The recombinant enzyme hydrolyzed carboxymethyl cellulose, swollen celluloses, chitosan and lichenan but not Avicel, chitin powder or xylan. With chitosan as the substrate, the optimum temperature and hydrolysis products of the recombinant enzyme varied at pH 4.0 and 8.0. This is the first report that characterizes chitosanase activity under different pH conditions.     

Expression, purification and characterization of two thermostable endoglucanases cloned from a lignocellulosic decomposing fungi Aspergillus fumigatus Z5 isolated from compost

Two genes encoding endoglucanase, designated as egl2 and egl3, were cloned from a lignocellulosic decomposing fungus Aspergillus fumigatus Z5 and were successfully expressed in Pichia pastoris X33. The deduced amino acid sequences encoded by egl2 and egl3 showed strong similarity with the sequence of glycoside hydrolase family 5. SDS-PAGE and western blot assays indicated that the recombinant enzymes were secreted into the culture medium and the zymogram analysis confirmed that both recombinant enzymes had endoglucanase activity. Several biochemical properties of the two recombinant enzymes were studied: Egl2 and Egl3 showed optimal activity at pH 5.0 and 4.0, respectively, and at 50 and 60°C, respectively. Egl2 and Egl3 showed good pH stability in the range of 4-7, and both enzymes demonstrated good thermostability ranging from 30 to 60°C. The K(m) and V(max) values using carboxymethyl cellulose (CMC, soluble cellulose, polymerized by β-1, 4-linked glucose residues) as the substrate at optimal conditions were determined. The activities of the enzymes on a variety of cello-oligosaccharide substrates were investigated, and Egl2 can hydrolyze cellotetraose and cellopentaose but not cellobiose and cellotriose, whereas Egl3 can hydrolyze all cello-oligosaccharides, except cellobiose.     

Mutanase from a Paenibacillus isolate: nucleotide sequence of the gene and properties of recombinant enzymes

A mutanase (alpha-1,3-glucanase)-producing microorganism was isolated from a soil sample and was identified as a relative of Paenibacillus sp. The mutanase was purified to homogeneity from culture, and its molecular mass was around 57 kDa. The gene for the mutanase was cloned by PCR using primers based on the N-terminal amino acid sequence of the purified enzyme. The determined nucleotide sequence of the gene consisted of 3651-bp open reading frame that encoded a predicted 1217-amino acid polypeptide including a 43-amino acid signal peptide. The mature enzyme showed similarity to mutanases RM1 of Bacillus sp. strain RM1 and KA-304 of Bacillus circulans with 65.6% and 62.7% identity, respectively. The predicted molecular mass of the mutanase was 123 kDa. Thus, the enzyme purified from the isolate appears to be truncated by proteolysis. The genes for the full-length and truncated mutanases were expressed in Bacillus subtilis cells, and the corresponding recombinant enzymes were purified to homogeneity. The molecular masses of the two enzymes were 116 and 57 kDa, respectively. The specific activity was 10-fold higher for the full-length enzyme than for the truncated enzyme. The optimal pH and temperature for both recombinant enzymes was pH 6.4 in citrate buffer and 45 degrees C to 50 degrees C. Amongst several tested polysaccharides, the recombinant full-length enzyme specifically hydrolyzed mutan.     

Plant succinic semialdehyde dehydrogenase. Cloning, purification, localization in mitochondria, and regulation by adenine nucleotides.

Succinic semialdehyde dehydrogenase (SSADH) is one of three enzymes constituting the gamma-aminobutyric acid shunt. We have cloned the cDNA for SSADH from Arabidopsis, which we designated SSADH1. SSADH1 cDNA encodes a protein of 528 amino acids (56 kD) with high similarity to SSADH from Escherichia coli and human (>59% identity). A sequence similar to a mitochondrial protease cleavage site is present 33 amino acids from the N terminus, indicating that the mature mitochondrial protein may contain 495 amino acids (53 kD). The native recombinant enzyme and the plant mitochondrial protein have a tetrameric molecular mass of 197 kD. Fractionation of plant mitochondria revealed its localization in the matrix. The purified recombinant enzyme showed maximal activity at pH 9.0 to 9.5, was specific for succinic semialdehyde (K(0.5) = 15 microM), and exclusively used NAD+ as a cofactor (Km = 130 +/- 77 microM). NADH was a competitive inhibitor with respect to NAD+ (Ki = 122 +/- 86 microM). AMP, ADP, and ATP inhibited the activity of SSADH (Ki = 2.5-8 mM). The mechanism of inhibition was competitive for AMP, noncompetitive for ATP, and mixed competitive for ADP with respect to NAD+. Plant SSADH may be responsive to mitochondrial energy charge and reducing potential in controlling metabolism of gamma-aminobutyric acid.     

Genetic and biochemical characterization of the Pseudoalteromonas tetraodonis alkaline κ-carrageenase

An alkaline κ-carrageenase, Cgk-K142, was found in the culture broth of a deep-sea bacterium, Pseudoalteromonas tetraodonis JAM-K142. A gene for the enzyme was cloned and expressed. Purified recombinant Cgk-K142 (rCgk-K142) showed an optimal pH of about 8.8 in glycine-NaOH buffer at 30 °C and of about 8.0 in MOPS buffer at 50 °C. The optimal temperature for the enzyme was 55 °C at pH 8.0. rCgk-K142 was unstable, but λ- and ι-carrageenans, non-degradative substrate homologs, extensively enhanced its stability. The nucleotide sequence of the gene for Cgk-K142 comprised 1,194 bp, and the deduced amino acid sequence (397 amino acids) showed a high level of similarity to the κ-carrageenase of P. carrageenovora, with 94% identity. Another gene for a κ-carrageenase-like protein was found downstream of the gene for Cgk-K142. The nucleotide sequence of that gene consisted of 966 bp (321 amino acids), and it showed the highest similarity, at 64% identity, to protein CgkB of P. carrageenovora, which has been reported as an incomplete 57-amino acid sequence.     

A new high-alkaline and high-molecular-weight pectate lyase from a Bacillus isolate: enzymatic properties and cloning of the gene for the enzyme

A pectate lyase (Pel; pectate transeliminase: EC4.2.2.2.), designated Pel-15H, was found in an alkaline culture of Bacillus sp. strain KSM-P15 and purified to homogeneity by sequential column chromatographies. The molecular weight of the enzyme determined by SDS-polyacrylamide gel electrophoresis was approximately 70,000 and the pI was around pH 4.6. Pel-15H randomly trans-eliminated polygalacturonate in the presence of Ca2+ ions, and the maximum activity was observed at pH 11.5 and at 55 degrees C in glycine-NaOH buffer. The gene for Pel-15H was cloned and sequenced, and the structural gene contained a 2,031-bp open reading frame that encoded 677 amino acids including a possible 28-amino-acid signal sequence. The mature enzyme (649 amino acids, molecular weight 69,550) showed very low similarity to Pels from Bacillus with 12.7-18.2% identity. Interestingly, part of the amino acid sequence of Pel-15H had fairly high similarity only to an N-terminal half of PelL and a C-terminal half of PeIX from Erwinia chrysanthemi 3937, and a C-terminal half of PeIX from E. chrysanthemi EC16 (approximately 35% identity for all).     

Functional characterization and differential expression studies of squalene synthase from Withania somnifera

Squalene synthase (SQS: EC 2.5.1.21) is a potential branch point regulatory enzyme and represents the first committed step to diverge the carbon flux from the main isoprenoid pathway towards sterol biosynthesis. In the present study, cloning and characterization of Withania somnifera squalene synthase (WsSQS) cDNA was investigated subsequently followed by its heterologous expression and preliminary enzyme activity. Two different types of WsSQS cDNA clones (WsSQS1and WsSQS2) were identified that contained an open reading frames of 1,236 and 1,242 bp encoding polypeptides of 412 and 414 amino acids respectively. Both WsSQS isoforms share 99 % similarity and identity with each other. WsSQS deduced amino acids sequences, when compared with SQS of other plant species, showed maximum similarity and identity with Capsicum annuum followed by Solanum tuberosum and Nicotiana tabacum. To obtain soluble recombinant enzymes, 24 hydrophobic amino acids were deleted from the carboxy terminus and expressed as 6X His-Tag fusion protein in Escherichia coli. Approximately 43 kDa recombinant protein was purified using Ni-NTA affinity chromatography and checked on SDS-PAGE. Preliminary activity of the purified enzymes was determined and the products were analyzed by gas chromatograph-mass spectrometer (GC-MS). Quantitative real-time PCR (qRT-PCR) analysis showed that WsSQS expresses more in young leaves than mature leaves, stem and root.     

Synthesis of Some Isocoumarin Derivatives

An alkaline κ-carrageenase, Cgk-K142, was found in the culture broth of a deep-sea bacterium, Pseudoalteromonas tetraodonis JAM-K142. A gene for the enzyme was cloned and expressed. Purified recombinant Cgk-K142 (rCgk-K142) showed an optimal pH of about 8.8 in glycine-NaOH buffer at 30 °C and of about 8.0 in MOPS buffer at 50 °C. The optimal temperature for the enzyme was 55 °C at pH 8.0. rCgk-K142 was unstable, but λ- and ι-carrageenans, non-degradative substrate homologs, extensively enhanced its stability. The nucleotide sequence of the gene for Cgk-K142 comprised 1,194 bp, and the deduced amino acid sequence (397 amino acids) showed a high level of similarity to the κ-carrageenase of P. carrageenovora, with 94% identity. Another gene for a κ-carrageenase-like protein was found downstream of the gene for Cgk-K142. The nucleotide sequence of that gene consisted of 966 bp (321 amino acids), and it showed the highest similarity, at 64% identity, to protein CgkB of P. carrageenovora, which has been reported as an incomplete 57-amino acid sequence.     

Rotihibin A,a Novel Plant Growth Regulator,from Streptomyces sp.

A thermophilic Thermoactinomyces sp. E79 producing a highly thermostable alkaline protease was isolated from soil. The protease, produced extracellularly by Thermoactinomyces sp. E79, was purified by DEAE-Sepharose CL-6B and Butyl-Toyopearl 650M column chromatography. The relative molecular mass was estimated to be 31,000 by SDS–polyacrylamide gel electrophoresis. Enzyme activity was inhibited by phenylmethylsulfonyl fluoride, suggesting the enzyme to be a serine protease. The optimum temperature for the enzyme activity was 85°C, and about 50% of the original activity remained after incubation at 90°C for 10 min in the presence of Ca^{2 +} . The optimum pH for the enzyme activity was 11.0 and the enzyme was fairly stable from pH 5.0 to 12.0. The gene for this thermostable alkaline protease was cloned in Escherichia coli and the expressed intracellular enzyme was activated by heat treatment. Sequence analysis showed an open reading frame of 1,152 base pairs, coding for a poiypeptide of 384 amino acids. The polypeptide was composed of a signal sequence (25 amino acids), a prosequence (81 amino acids), and a mature protein of 278 amino acids. The deduced amino acid sequence of the mature protease had high similarity with thermitase, a serine protease from Thermoactinomyces vulgaris, and the extent of sequence identity was 76%.     

Cloning and overexpression of a Paenibacillus beta-glucanase in Pichia pastoris: purification and characterization of the recombinant enzyme

Isolation, expression, and characterization of a novel endo-beta-1,3(4)-D-glucanase with high specific activity and homology to Bacillus lichenases is described. One clone was screened from a genomic library of Paenibacillus sp. F-40, using lichenan-containing plates. The nucleotide sequence of the clone contains an ORF consisting of 717 nucleotides, encoding a beta-glucanase protein of 238 amino acids and 26 residues of a putative signal peptide at its N-terminus. The amino acid sequence showed the highest similarity of 87% to other beta-1,3-1,4-glucanases of Bacillus. The gene fragment Bg1 containing the mature glucanase protein was expressed in Pichia pastoris at high expression level in a 3-1 high-cell-density fermenter. The purified recombinant enzyme Bgl showed activity against barley beta-glucan, lichenan, and laminarin. The gene encodes an endo-beta-1,3(4)-D-glucanase (E. C. 3.2.1.6). When lichenan was used as substrate, the optimal pH was 6.5, and the optimal temperature was 60 degrees C. The K(m), V(max), and k(cat) values for lichenan are 2.96 mg/ml, 6,951 micromol/min x mg, and 3,131 s(-1), respectively. For barley beta-glucan the values are 3.73 mg/ml, 8,939 micromol/min x mg, and 4,026 s(-1), respectively. The recombinant Bg1 had resistance to pepsin and trypsin. Other features of recombinant Bg1 including temperature and pH stability, and sensitivity to some metal ions and chemical reagents were also characterized.     

Structure and characteristics of an endo-beta-1,4-glucanase, isolated from Trametes hirsuta, with high degradation to crystalline cellulose

Trametes hirsuta produced cellulose-degrading enzymes when it was grown in a cellulosic medium such as Avicel or wheat bran. An endo-beta-1,4-glucanase (ThEG) was purified from the culture filtrate, and the gene and the cDNA were isolated. The gene consisted of an open reading frame encoding 384 amino acids, interrupted by 11 introns. The whole sequence showed high homology with that of family 5 glycoside hydrolase. The properties of the recombinant enzyme (rEG) in Aspergillus oryzae were compared with those of the En-1 from Irpex lacteus, which showed the highest homology among all the endoglucanases reported. The rEG activity against Avicel was about 8 times higher than that of En-1 when based on CMC degradation. A remarkable structural difference between the two enzymes was the length of the linker connecting the cellulose-binding domain to the catalytic domain.     

Truncation of the cellulose binding domain improved thermal stability of endo-beta-1,4-glucanase from Bacillus subtilis JA18

The C-terminus region of endo-beta-glucanase Egl499 from Bacillus subtilis JA18 was suggested to be a putative family 3 cellulose-binding domain (CBD) by computer analysis. To prove this proposal, C-terminus truncation mutant Egl330 was constructed and expressed. Compared with Egl499, Egl330 lost the cellulose binding capability at 4 degrees C, confirming the C-terminus region was a CBD. Binding of the CBD to Avicel was inhibited by carboxymethylcellulose (CMC), but not by barley beta-glucan and glucose at concentration of 0.1% and 0.5%. Kinetic analysis showed both the turnover rate (k(cat)) and the catalytic efficiency (k(cat)/K(m)) of Egl330 increased for the substrate CMC compared to Egl499. A great improvement in thermal stability was observed in Egl330. The half life of Egl330 at 65 degrees C increased to three folds that of Egl499, from 10 to 29 min. After treated at 80 degrees C for 10 min, Egl330 could recover more than 60% of its original activity while Egl499 only recovered 12% activity. UV spectrometry analysis showed Egl330 and Egl499 differed in refolding efficiency after heat treatment.     

Cloning and expression of cyclodextrin glycosyltransferase gene from Paenibacillus sp. T16 isolated from hot spring soil in northern Thailand

Gene encoding cyclodextrin glycosyltransferase (CGTase), from thermotolerant Paenibacillus sp. T16 isolated from hot spring area in northern Thailand, was cloned and expressed in E. coli (JM109). The nucleotide sequences of both wild type and transformed CGTases consisted of 2139 bp open reading frame, 713 deduced amino acids residues with difference of 4 amino acid residues. The recombinant cells required 24 h culture time and a neutral pH for culture medium to produce compatible amount of CGTase compared to 72 h culture time and pH 10 for wild type. The recombinant and wild-type CGTases were purified by starch adsorption and phenyl sepharose column chromatography and characterized in parallel. Both enzymes showed molecular weight of 77 kDa and similar optimum pHs and temperatures with recombinant enzyme showing broader range. There were some significant difference in pH, temperature stability and kinetic parameters. The presence of high starch concentration resulted in higher thermostability in recombinant enzyme than the wild type. The recombinant enzyme was more stable at higher temperature and lower pH, with lower K(m) for coupling reaction using cellobiose and cyclodextrins as substrates.     

Identification and expression of cellobiohydrolase (CBHI) gene from an endophytic fungus, Fusicoccum sp. (BCC4124) in Pichia pastoris

A gene encoding a cellobiohydrolase (CBHI) was isolated from Fusicoccum sp. (BCC4124), an endophytic fungus belongs in phylum Ascomycota, using 5' and 3' rapid amplification of cDNA end (RACE) technique. This CBHI gene contains 1395 nucleotides and encodes a 465-amino acid protein with a molecular weight of approximately 50 kDa. The deduced amino acid sequence showed significant similarity to those of other fungal CBHI belonging to family 7 of glycosyl hydrolase. Interestingly, the result from the amino acid alignment revealed that this CBHI does not contain the cellulose binding domain nor the linker region. The CBHI gene was successfully expressed in Pichia pastoris KM71. The purified recombinant CBHI has ability to hydrolyze Avicel, filter paper and 4-methylumbelliferyl beta-d-cellobioside (MUC) but not carboxymethylcellulose (CMC). It showed an optimal working condition at 40 degrees C, pH 5 with K(m) and V(max) toward MUC of 0.57 mM and 3.086 nmol/min/mg protein, respectively. The purified enzyme was stable at pH range of 3-11. The enzyme retained approximately 50% of its maximal activity after incubating at 70-90 degrees C for 30 min. Due to its stability through wide range of pH, and moderately stable at high temperature, this enzyme has potential in various biotechnology applications.     

Induction of a Metallothionein-like Protein in Tetrahymena pyriformis by Metal Ions

Trametes hirsuta produced cellulose-degrading enzymes when it was grown in a cellulosic medium such as Avicel or wheat bran. An endo-β-1,4-glucanase (ThEG) was purified from the culture filtrate, and the gene and the cDNA were isolated. The gene consisted of an open reading frame encoding 384 amino acids, interrupted by 11 introns. The whole sequence showed high homology with that of family 5 glycoside hydrolase. The properties of the recombinant enzyme (rEG) in Aspergillus oryzae were compared with those of the En-1 from Irpex lacteus, which showed the highest homology among all the endoglucanases reported. The rEG activity against Avicel was about 8 times higher than that of En-1 when based on CMC degradation. A remarkable structural difference between the two enzymes was the length of the linker connecting the cellulose-binding domain to the catalytic domain.     

Gene cloning,sequencing, and expression of an esterase from Acinetobacter lwoffii I6C-1

The esterase-encoding gene, estA, was cloned from Acinetobacter lwoffii I6C-1 genomic DNA into Escherichia coli BL21(DE3) with plasmid vector pET-22b (pEM1). pEM1 has a 4.4-kb EcoRI insert that contained the complete estA gene. A 2.4-kb AvaI- SphI DNA fragment was subcloned (pEM3) and sequenced. estA gene encodes a protein of 366 amino acids (40,687 Da) with a pI of 9.17. The EstA signal peptide was 31 amino acids long, and the mature esterase sequence is 335 amino acids long (37.5 kDa). The conserved catalytic serine residue of EstA is in position 210. The EstA sequence was similar to that of the carboxylesterase from Acinetobacter calcoaceticus (75% identity, 85% similarity), Archaeoglobus fulgidus (37% identity, 59% similarity), and Mycobacterium tuberculosis (35% identity, 51% similarity). These enzymes contained the conserved motif G-X(1)-S-X(2)-G carrying the active-site serine of hydrolytic enzyme. The EstA activity in A. lwoffii I6C-1 remains constant throughout the stationary phase, and the activity in E. coil BL21 (DE3) with pEM1 was similar to A. lwoffii I6C-1.     

A comparative analysis of two cDNA clones of the cellulase gene family from anaerobic fungus Piromyces rhizinflata

Cellulase family and some other glycosyl hydrolases of anaerobic fungi inhabiting the digestive tract of ruminants are believed to form an enzyme complex called cellulosome. Study of the individual component of cellulosome may shed light on understanding the organization of this complex and its functional mechanism. We have analysed the primary sequences of two cellulase clones, cel5B and cel6A, isolated from the cDNA library of ruminal fungus, Piromyces rhizinflata strain 2301. The deduced amino acid sequences of the catalytic domain of Cel5B, encoded by cel5B, showed homology with the subfamily 4 of the family 5 (subfamily 5(4)) of glycosyl hydrolases, while cel6A encoded Cel6A belonged to family 6 of glycosyl hydrolases. Phylogenetic tree analysis suggested that the genes of subfamily 5(4) glycosyl hydrolases of P. rhizinflata might have been acquired from rumen bacteria. Cel5B and Cel6A were modular enzymes consisting of a catalytic domain and dockerin domain(s), but not a cellulose binding domain. The occurrence of dockerin domains indicated that both enzymes were cellulosome components. The catalytic domain of the Cel5B (Cel5B') and Cel6A (Cel6A') recombinant proteins were purified. The optimal activity conditions with carboxymethyl cellulose (CMC) as the substrate were pH 6.0 and 50 degrees C for Cel5B', and pH 6.0 and 37-45 degrees C for Cel6A'. Both Cel5B' and Cel6A' exhibited activity against CMC, barley beta-glucan, Lichenan, and oat spelt xylan. Cel5B' could also hydrolyse p-nitrophenyl-beta-d-cellobioside, Avicel and filter paper while Cel6A' did not show any activity on these substrates. It is apparent that Cel6A' acted as an endoglucanase and Cel5B' possessed both endoglucanase and exoglucanase activities. No synergic effect was observed for these recombinant enzymes in vitro on Avicel and CMC.     

Spatial separation of protein domains is not necessary for catalytic activity or substrate binding in a xylanase.

Xylanase A (XYLA) from Pseudomonas fluorescens subspecies cellulosa shows sequence conservation with two endoglucanases from the same organism. The conserved sequence in XYLA, consisting of the N-terminal 234 residues, is not essential for catalytic activity. Full-length XYLA and a fusion enzyme, consisting of the N-terminal 100 residues of XYLA linked to mature alkaline phosphatase, bound tightly to crystalline cellulose (Avicel), but not to xylan. The capacity of truncated derivatives of the xylanase to bind polysaccharides was investigated. XYLA lacking the first 13 N-terminal amino acids did not bind to cellulose. However, a catalytically active XYLA derivative (XYLA'), in which residues 100-234 were deleted, bound tightly to Avicel. Substrate specificity, cellulose-binding capacity, specific activity and Km for xylan hydrolysis were evaluated for each of the xylanases. No differences in any of these parameters were detected for the two enzymes. It is concluded that XYLA contains a cellulose-binding domain consisting of the N-terminal 100 residues which is distinct from the active site. Spatial separation of the catalytic and cellulose-binding domains is not essential for the enzyme to function normally.