Purification and biochemical properties of an alkaline pullulanase from alkalophilic Bacillus sp. S-1

A novel extracellular pullulanase (PUL-E, pullulan 6-glucanohydrolase, EC 3.2.1.41) has been purified from the alkalophilic Bacillus sp. S-1. The purified enzyme had a molecular mass of about 140 kDa on denaturated and natural conditions. The pI was 5.5. The pullulanase, when resolved by SDS-PAGE, was negative for Schiff staining, suggesting that the enzyme is not a glycoprotein. The N-terminal amino acid sequence of the enzyme was Phe-Leu-Asn-Met-Ser-(Trp-Phe). The enzyme displayed a temperature optimum of around 60 degrees C and a pH optimum of around pH 9.0. The enzyme was stable to incubation from pH 4.0 to pH 11.0 at 4 degrees C for 24 h. The presence of pullulan protected the enzyme from heat inactivation, the extent depending upon the substrate concentration. The activity of the enzyme was stimulated by Mn2+ ions. Ca2+ ions and EDTA did not inhibit the enzyme activity. The enzyme hydrolyzed the alpha-1,6-linkages of amylopectin, glycogens, alpha,beta-limited dextrin, and pullulan. The enzyme had an apparent Km of 7.92 mg/ml for pullulan, a Km of 1.63 mg/ml for amylopectin, and a Km of 3.1 mg/ml for alpha,beta-limited dextrin, when measured at pH 9.0 and 50 degrees C. The enzyme caused the complete hydrolysis of pullulan to maltotriose. The activity was not inhibited by alpha, beta, or gamma-cyclodextrins. The western blotting analysis with mouse anti-serum against PUL-E showed that PUL-E is produced as a single enzyme form during bacterial cultivation.

Cloning and sequencing of a gene encoding acidophilic amylase from Bacillus acidocaldarius

Two starch-degrading enzymes produced by Bacillus acidocaldarius (renamed as Alicyclobacillus acidocaldarius) were identified. According to SDS-PAGE, the apparent molecular masses of the enzymes were 90 and 160 kDa. Eight peptide fragments and the N-terminal end of the 90 kDa polypeptide were sequenced. An oligonucleotide, based on the amino acid sequence of a peptide fragment of the 90 kDa protein, was used to screen a lambda gt10 bank of B. acidocaldarius, and the region encoding the 90 kDa protein was cloned. Unexpectedly, the ORF continued upstream of the N terminus of the 90 kDa protein. The entire ORF was 1301 amino acids (aa) long (calculated molecular mass 140 kDa) and it was preceded by a putative ribosomal binding site and a promoter. Computer analysis showed that the 1301 aa protein was closely related to an alpha-amylase-pullulanase of Clostridium thermohydrosulfuricum. We suggest that the starch-degrading 160 kDa protein of B. acidocaldarius is an alpha-amylase-pullulanase, and the 90 kDa protein is a cleavage product of the 160 kDa protein. Another ORF, apparently in the same transcription unit, was found downstream from the amylase gene. It encoded a protein that was closely related to the maltose-binding protein of Escherichia coli.

Identification of the gene encoding the major cellobiohydrolase of the white rot fungus Phanerochaete chrysosporium

Previous studies have shown that the cellobiohydrolases of the white rot basidiomycete Phanerochaete chrysosporium are encoded by a family of structurally related genes. In this investigation, we identified and sequenced the most highly transcribed gene, cbh1-4. Evidence suggests that in this fungus the dominant isozyme, CBH1, is encoded by chb1-4.

Arabinan degrading enzymes from Aspergillus nidulans: induction and purification

The presence in Aspergillus nidulans of two enzymes related to the Aspergillus niger endo-arabinase and alpha-L-arabinofuranosidase B has been established using antibodies against the purified A. niger enzymes. Moreover, the absence of an equivalent in A. nidulans to the alpha-L-arabinofuranosidase A of A. niger has been confirmed both at the protein and at the DNA level. Both A. nidulans arabinases have been purified and physico-chemically and kinetically characterized. They have a much higher temperature optimum than the corresponding A. niger enzymes. The pattern of induction has been studied on media containing different carbon sources showing an important role of L-arabitol in the induction of these enzymes.

Crystallization and preliminary X-ray analysis of two major xylanases from Trichoderma reesei

Two major endoxylanases, endo-beta-1,4-xylanase I and II (molecular mass 19 kDa and 21 kDa) from the filamentous fungus Trichoderma reesei have been crystallized by using ammonium sulphate as the precipitating agent. Both crystals were monoclinic and belonged to the space groups C2 (a = 71.9 A, b = 39.0 A, c = 59.9 A, beta = 118.0 degrees, for XYNI) and P2(1) (a = 81.6 A, b = 60.6 A, c = 38.3 A, beta = 94.4, for XYNII). The crystals diffract to at least 2.2 A and 1.5 A, respectively.

Determinants for the enhanced thermostability of hybrid (1-3,1-4)-beta-glucanases

Hybrid (1-3,1-4)-beta-glucanases which contain an N-terminal region derived from the Bacillus amyloliquefaciens enzyme and a C-terminal region of the closely related B. macerans enzyme may exhibit a thermostability superior to both parental enzymes. A systematic series of hybrid enzymes were constructed in order to delineate the amino acid residues that affect protein stability. Hybrid enzymes with between one and four of the N-terminal residues for the mature B. amyloliquefaciens (1-3,1-4)-beta-glucanase exhibit no significant changes in biochemical characteristics as compared with the parental B. macerans enzyme. However, significantly enhanced thermostability was observed in the hybrid enzyme containing an N-terminal segment of eight amino acid residues derived from the B. amyloliquefaciens enzyme. Site-directed mutagenesis revealed that the combined effect of Gln1, Thr2, Ser5 and Phe7 confer enhanced stability on hybrid enzymes, probably by improving the hydrogen bonding that stabilizes the interactions between the N-terminal and the centre of the folded molecule, as well as between the two termini of the polypeptide chain. Furthermore, deletion of Tyr13 in the hybrid enzyme containing the 12 N-terminal amino acids from the B. amyloliquefaciens (1-3,1-4)-beta-glucanase results in a dramatic increase in stability at 70 degrees C with the half-life of 6 min increased to around 4 h. This is twofold higher than the hitherto most stable hybrid enzyme in which the N-terminal domain consisted of 16 residues of the B. amyloliquefaciens enzyme.

Purification and characterization of an enzyme releasing lacto-N-biose from oligosaccharides with type 1 chain

An enzyme specific for oligosaccharides with type 1 chain was purified 7,000-fold from the culture broth of Streptomyces sp. 142. The enzyme, lacto-N-biosidase, was induced and secreted into culture medium when the strain was cultured in the presence of porcine stomach mucin. The enzyme was purified by anion-exchange chromatography on Q Sepharose, cation-exchange chromatography on S Sepharose, fast protein liquid chromatography on a Mono S column, and gel filtration chromatography on TSK gel HW55S. To remove contaminating alpha-1,3/4-fucosidase and beta-N-acetylglucosaminidase, final purification was done by fast protein liquid chromatography on a Mono S column and affinity chromatography on N-acetylglucosamine agarose. The purified enzyme gave only one major protein band with an apparent M(r) of 60,000 on sodium dodesyl sulfate-polyacrylamide gel electrophoresis. The enzyme had maximum activity at pH 5.5 and was stable at the pH range of 4.0-10.0. Substrate specificity studies with oligosaccharides labeled with 2-aminopyridine showed that the enzyme specifically hydrolyzed lacto-N-tetraose and the N-acetyllactosamine type of triantennary sugar chain with the type 1 chain, but did not hydrolyze type 2 chain oligosaccharides or the type 1 chain oligosaccharides with fucose or sialic acid including lacto-N-fucopentaose I and II and alpha-2,3-sialyl lacto-N-tetraose. The enzyme released lacto-N-biose from asialofetuin, and almost all oligosaccharides in asialofetuin were found to have only type 2 chains. Sequential digestion of extended type 1 chain oligosaccharides with alpha-1,3/4-fucosidase and lacto-N-biosidase was possible.

Characterization of the active site and thermostability regions of endoxylanase from Thermoanaerobacterium saccharolyticum B6A-RI

Deletion mutants were constructed from pZEP12, which contained the intact Thermoanaerobacterium saccharolyticum endoxylanase gene (xynA). Deletion of 1.75 kb from the N-terminal end of xynA resulted in a mutant enzyme that retained activity but lost thermostability. Deletion of 1.05 kb from the C terminus did not alter thermostability or activity. The deduced amino acid sequence of T. saccharolyticum B6A-RI endoxylanase XynA was aligned with five other family F beta-glycanases by using the PILEUP program of the Genetics Computer Group package. This multiple alignment of amino acid sequences revealed six highly conserved motifs which included the consensus sequence consisting of a hydrophobic amino acid, Ser or Thr, Glu, a hydrophobic amino acid, Asp, and a hydrophobic amino acid in the catalytic domain. Endoxylanase was inhibited by EDAC [1-(3-dimethylamino propenyl)-3-ethylcarbodiimide hydrochloride], suggesting that Asp and/or Glu was involved in catalysis. Three aspartic acids, two glutamic acids, and one histidine were conserved in all six enzymes aligned. Hydrophobic cluster analysis revealed that two Asp and one Glu occur in the same hydrophobic clusters in T. saccharolyticum B6A-RI endoxylanase and two other enzymes belonging to family F beta-glycanases and suggests their involvement in a catalytic triad. These two Asp and one Glu in XynA from T. saccharolyticum were targeted for analysis by site-specific mutagenesis. Substitution of Asp-537 and Asp-602 by Asn and Glu-600 by Gln completely destroyed endoxylanase activity. These results suggest that these three amino acids form a catalytic triad that functions in a general acid catalysis mechanism.

Structure and function of proteins of the phosphotransferase system and of 6-phospho-beta-glycosidases in gram-positive bacteria

New information about the proteins of the phosphotransferase system (PTS) and of phosphoglycosidases of homofermentative lactic acid bacteria and related species is presented. Tertiary structures were elucidated from soluble PTS components. They help to understand regulatory processes and PTS function in lactic acid bacteria. A tertiary structure of a membrane-bound enzyme II is still not available, but expression of Gram-positive genes encoding enzymes II can be achieved in Escherichia coli and enables the development of effective isolation procedures which are necessary for crystallization experiments. Considerable progress was made in analysing the functions of structural genes which are in close vicinity of the genes encoding the sugar-specific PTS components, such as the genes encoding the tagatose-6-P pathway and the 6-phospho-beta-glycosidases. These phosphoglycosidases belong to a subfamily of the beta-glycosidase family I among about 300 different glycosidases. The active site nucleophile was recently identified to be Glu 358 in Agrobacterium beta-glucosidase. This corresponds to Glu 375 in staphylococcal and lactococcal 6-phospho-beta-galactosidase. This enzyme is inactivated by mutating Glu 375 to Gln. Diffracting crystals of the lactococcal 6-P-beta-galactosidase allow the elucidation of its tertiary structure which helps to derive the structures for the entire glycosidase family 1. In addition, a fusion protein with 6-phospho-beta-galactosidase and staphylococcal protein A was constructed.

Crystallization and preliminary X-ray diffraction analysis of crystals of Thermoascus aurantiacus xylanase

Crystals suitable for high resolution X-ray diffraction analysis have been grown of the 29,774-Da protein, xylanase (1,-4-beta-xylan xylanohydrolase EC 3.2.1.8) from the thermophilic fungus Thermoascus aurantiacus. This protein, an endoxylanase demonstrates the hydrolysis of beta-(1-4)-D-xylose linkage in xylans and crystallizes as monoclinic pinacoids in the presence of ammonium sulphate buffered at pH 6.5, and also with neutral polyethylene glycol 6000. The crystals belong to space group P2(1) and have cell dimensions, a = 41.2 A, b = 67.76 A, c = 51.8 A; beta = 113.2 degrees.

Crystallization of barley (1-3,1-4)-beta-glucanase, isoenzyme II

The (1-3,1-4)-beta-glucanase from barley (Hordeum vulgare, cv Alexis) degrades mixed linked beta-glucan in the cell wall of the starchy endosperm. Isoenzyme II of the (1-3,1-4)-beta-glucanase forms large single crystals when a protein solution is equilibrated against 20% (w/w) polyethylene glycol 8000 at acidic pH using the hanging drop vapour diffusion method. The crystals diffract to better than 2 A resolution. They are monoclinic, space group P2(1), with cell dimensions a = 49.58 A, b = 82.99 A, c = 77.56 A and beta = 104.36 degrees. Two protein molecules are estimated to fill the asymmetric unit.

Crystallization of a chitosanase from Streptomyces N174

Chitosanases are produced by many soil fungi and bacteria to degrade chitosan present in fungal cell walls. Here, we report the crystallization of a 29,500 dalton protein with chitosan endo-hydrolase activity isolated from Streptomyces N174. The crystals were grown by vapor diffusion. They are mechanically strong and diffract to at least 1.9 A resolution. The crystals belong to the monoclinic space group P2(1) with unit cell parameters a = 56.4 A, b = 59.6 A, c = 86.1 A and beta = 96.6 degrees. Cell parameters and crystal density are consistent with two chitosanase molecules per asymmetric unit.

New families in the classification of glycosyl hydrolases based on amino acid sequence similarities

301 glycosyl hydrolases and related enzymes corresponding to 39 EC entries of the I.U.B. classification system have been classified into 35 families on the basis of amino-acid-sequence similarities [Henrissat (1991) Biochem. J. 280, 309-316]. Approximately half of the families were found to be monospecific (containing only one EC number), whereas the other half were found to be polyspecific (containing at least two EC numbers). A > 60% increase in sequence data for glycosyl hydrolases (181 additional enzymes or enzyme domains sequences have since become available) allowed us to update the classification not only by the addition of more members to already identified families, but also by the finding of ten new families. On the basis of a comparison of 482 sequences corresponding to 52 EC entries, 45 families, out of which 22 are polyspecific, can now be defined. This classification has been implemented in the SWISS-PROT protein sequence data bank.

Three forms of cellobiohydrolase I from Trichoderma reesei

Three forms of cellobiohydrolase I (CBH I) (65, 58 and 54 kDa) were isolated to apparent homogeneity from culture filtrates of Trichoderma reesei. The N-terminal sequence of amino acid residues is the same for all of them. The 65 kDa CBH I (pI 4.1) is the intact protein which is fully active against small, soluble substrates and an insoluble substrate Avicel. The 58 kDa CBH I (pI 3.8) and 54 kDa CBH I (pI 3.6) are two truncated forms of the intact CBH I, which are fully active against small, soluble substrates, but have decreased adsorption on and activity against Avicel. Limited proteolysis of the 65 kDa and 58 kDa CBH I by papain yields the same core protein (pI 3.6, 54 kDa). It appears that there are mainly two different specific proteolytic cleavage points in the intact CBH I, one the site for a papain-like protease action cutting at the hinge area (54 kDa CBH I) and the other in the B block (58 kDa CBH I).

Folding and assembly of phage P22 tailspike endorhamnosidase lacking the N-terminal, head-binding domain

Tryptic digestion of a thermal unfolding intermediate of the phage P22 tailspike endorhamnosidase produces an N-terminally shortened protein fragment comprising amino-acid residues 108-666 [Chen, B.-L. & King, J. (1991) Biochemistry 30, 6260-6269]. In the present work, the 60-kDa C-terminal fragment was purified to homogeneity from the tryptic digest by gel-fitration chromatography. As in the case for the whole tailspike protein (72 kDa), the purified fragment was found to remain stably folded as a highly soluble, SDS-resistant, enzymatically active trimer. However, its unfolding in the presence of guanidinium chloride was accelerated at least 10-fold compared to the complete, native tailspike protein. Shortened tailspike trimers reconstituted spontaneously and with high yield after diluting a solution containing acid-urea-unfolded fragment polypeptides with neutral buffer. Upon recombinant expression of the 60-kDa polypeptide in Escherichia coli, it also assembled efficiently and formed SDS-resistant trimers. The refolding and assembly pathway of the N-terminally shortened tailspike paralleled that of the complete protein with slightly, but significantly, accelerated folding reactions, at both the subunit and the trimer levels. As found for the complete tailspike protein, yields of refolding and assembly of the 60-kDa fragments into SDS-resistant trimers decreased with increasing temperature. The refolding yield of fragments derived from a temperature-sensitive mutant (Gly244-->Arg) tailspike protein was affected in similar fashion as shown for the whole protein. We conclude that the N-terminal domain (residues 1-107) is dispensable for folding and assembly of the P22 tailspike endorhamnosidase both in vitro and in vivo.

Modification of oligosaccharide antenna flexibility induced by exoglycosidase trimming

We have investigated the solution conformation of a triantennary glycopeptide using resonance energy transfer [Rice et al. (1991) Biochemistry 30, 6646-6655]. Triantennary glycopeptide was derivatized with a donor fluorophore on the N-terminus and with an acceptor fluorophore attached individually to each terminal galactose residue, resulting in three isomeric donor-acceptor pairs. Time-resolved energy-transfer experiments revealed two distinct donor-acceptor distance populations for two of the three antennae of the oligosaccharide. An extended conformation and a folded conformation were detected for the two flexible antennae whereas the third antenna on the oligosaccharide was rigid, containing only an extended conformer. The ratios of the extended to folded conformers of the two flexible antennae were reversibly modulated by temperature, allowing the calculation of delta H and delta S for the conformational change [Wu et al. (1991) Proc. Natl. Acad. Sci. U.S.A. 88, 9355-9359]. In the present study, we have trimmed the fluorescent glycopeptides with exoglycosidases which specifically removed the unmodified antennae of the oligosaccharide. The resulting single-chain isomeric glycopeptides each contained identical core sugar residues and a terminally located donor and acceptor, but differed only in the linkage configuration of the sugar residues. Analysis of these glycopeptides by time-resolved energy transfer indicated that each antenna of the oligosaccharide is, by itself, maintained exclusively in the extended conformation. Temperature modulation failed to induce antenna folding as was previously observed for the complete triantennary structure. These data suggest that interantenna interactions modulate the conformation of individual antenna of complex oligosaccharides.

Purification and some properties of intracellular alpha-L-arabinofuranosidase from Aspergillus niger 5-16

alpha-L-Arabinofuranosidase was purified from a cell-free extract of Aspergillus niger 5-16 by chromatographies on DEAE-Toyopearl, SP-Toyopearl, Ultro-gel AcA 44, Mono P, and TSK-Gel G3000SW. The final preparation thus obtained showed a single band on SDS-polyacrylamide gel electrophoresis. The molecular weight and isoelectric point were 67,000 by SDS-polyacrylamide gel electrophoresis and pH 3.5 by isoelectric focusing. The alpha-L-arabinofuranosidase contained amino acids in the order of Asx > Gly > Ala > Thr > Glx = Ser. The enzyme had maximum activity at pH 4.0 and 60 degrees C, and was stable from pH 4 to 7 and at temperatures up to 30 degrees C. The enzyme activity was not affected considerably by either metal ions or chemical reagents. The enzyme released arabinose from p-nitrophenyl-alpha-L-arabinofuranoside, O-alpha-L-arabinofuranosyl-(1-->3)-O-beta-D-xylopyranosyl-(1-->4)-D- xylopyranose, and arabinan, but not from O-beta-D-xylopyranosyl-(1-->4)-O-[alpha-L-arabinofuranosyl- (1-->3)]-O-beta-D-xylopyranosyl-(1-->4)-D-xylopyranose, O-beta-D-xylopyranosyl-(1-->2)-O-alpha-L-arabinofuranosyl-(1-->3)-O-beta -D- xylopyranosyl-(1-->4)-O-beta-D-xylopyranosyl-(1-->4)-D-xylopyranose, gum arabic, or arabinoxylan. The limit of hydrolysis of arabinan was about 58% even when the enzyme was sufficiently in excess.

Purification and some properties of an alkaline xylanase from alkaliphilic Bacillus sp. strain 41M-1

An alkaliphilic Bacillus sp. strain, 41M-1, isolated from soil produced multiple xylanases extracellularly. One of these xylanases was purified to homogeneity by ammonium sulfate fractionation and anion-exchange chromatography. The moleculr mass of this enzyme (xylanase J) was 36 kDa, and the isoelectric point was pH 5.3. Xylanase J was most active at pH 9.0. The optimum temperature for the activity at pH 9.0 was around 50 degrees C. The enzyme was stable up to 55 degrees C at pH 9.0 for 30 min. Xylanase J was completely inhibited by the Hg2+ion and N-bromosuccinimide. The predominant products of xylan hydrolysate were xylobiose, xylotriose, and higher oligosaccharides, indicating that the enzyme was an endoxylanase. The apparent Km and Vmax values on xylan were 3.3 mg/ml and 1,100 micromol-1 mg-1, respectively. Xylanase J showed high sequence homology with the xylanases from Bacillus pumilus and Clostridium acetobutylicum in the N-terminal region. Xylanase J acted on neither crystalline cellulose nor carboxymethyl cellulose, indicating a possible application of the enzyme in biobleaching processes.

Evolution of polysaccharide hydrolase substrate specificity. Catalytic amino acids are conserved in barley 1,3-1,4- and 1,3-beta-glucanases

Catalytic amino acid residues in a 1,3-beta-D-glucan 3-glucanohydrolase (EC 3.2.1.39) and a homologous 1,3-1,4-beta-D-glucan 4-glucanohydrolase (EC 3.2.1.73) from barley have been investigated. To identify amino acids responsible for protonation of the glycosidic oxygen during hydrolysis, carbodiimide-mediated labeling of the enzymes with [14C]glycine ethyl ester was performed. This resulted in loss of activity and specific modification of the Glu288 residues in both enzymes. The stoichiometry of labeling was approximately 1:1, and modification was reduced in the presence of substrate analogues. Based on these data, the Glu288 residues are likely to be present at the active sites of the respective enzymes and may represent the catalytic acids in the hydrolytic reaction. The catalytic nucleophiles of the two enzymes were investigated by labeling with specific, mechanism-based epoxyalkyl-beta-oligoglucosides. Amino acid residues Glu232 and Glu231 were identified as the likely catalytic nucleophiles in the 1,3-1,4- and 1,3-beta-glucanases, respectively. Thus the position of the catalytic nucleophile and the putative proton donating amino acids in the two classes of beta-glucan endohydrolases are conserved. The acquisition of distinct substrate specificities in the evolution of these related enzymes may therefore not require the recruitment of novel catalytic amino acids but rather differences in their positioning at the active site and/or changes in substrate binding residues.

Purification and characterization of the alpha-agarase from Alteromonas agarlyticus (Cataldi) comb. nov., strain GJ1B

The phenotypic features of strain GJ1B, an unidentified marine bacterium that degrades agar [Young, K. S. Bhattacharjee, S. S. & Yaphe, W. (1978) Carbohydr. Res. 66, 207-212], were investigated and its agarolytic system was characterized using 13C-NMR spectroscopy to analyse the agarose degradation products. The bacterium was assigned to the genus Alteromonas and the new combination A. agarlyticus (Cataldi) is proposed. An alpha-agarase, i.e. specific for the alpha(1-->3) linkages present in agarose, was purified to homogeneity from the culture supernatant by affinity chromatography on cross-linked agarose (Sepharose CL-6B) and by anion-exchange chromatography (Mono Q column). The major end product of agarose hydrolysis using the purified enzyme was agarotetraose. Using SDS/PAGE, the purified alpha-agarase was detected as a single band with a molecular mass of 180 kDa. After the affinity-chromatography step, however, the native molecular mass was approximately 360 kDa, suggesting that the native enzyme is a dimer which is dissociated to active subunits by anion-exchange chromatography. The isolectric point was estimated to be 5.3. Enzyme activity was observed using agar as the substrate over the pH range 6.0-9.0 with a maximum value at pH 7.2 in Mops or Tris buffer. The enzyme was inactivated by prolonged treatment at a pH below 6.5, or by temperatures over 45 degrees C or by removing calcium. In addition, a beta-galactosidase specific for the end products of the alpha-agarase was present in the alpha-agarase affinity-chromatography fraction, probably as part of a complex with this enzyme. The degradation of agarose by this agarase complex yielded a mixture of oligosaccharides in the agarotetraose series and the agarotriose series, the latter consisting of oligosaccharides with an odd number of galactose residues.

Purification and characterization of a thermostable xylanase from Bacillus stearothermophilus T-6

Bacillus stearothermophilus T-6 produces an extracellular xylanase that was shown to optimally bleach pulp at pH 9 and 65 degrees C. The enzyme was purified and concentrated in a single adsorption step onto a cation exchanger and is made of a single polypeptide with an apparent M(r) of 43,000 (determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis). Xylanase T-6 is an endoxylanase that completely degrades xylan to xylose and xylobiose. The pIs of the purified protein were 9 and 7 under native and denaturing conditions, respectively. The optimum activity was at pH 6.5; however, 60% of the activity was still retained at pH 10. At 65 degrees C and pH 7, the enzyme was stable for more than 10 h; at 65 degrees C and pH 9, the half-life of the enzyme was approximately 6 h. Kinetic experiments at 55 degrees C gave Vmax and Km values of 288 U/mg and 1.63 mg/ml, respectively. The enzyme had no apparent requirement for cofactors, and its activity was strongly inhibited by Zn2+, Cd2+, and Hg2+. Xylan completely protected the protein from inactivation by N-bromosuccinimide. The N-terminal sequence of the first 45 amino acids of the enzyme showed high homology with the N-terminal region of xylanase A from the alkalophilic Bacillus sp. strain C-125.

Sequence analysis of scrA and scrB from Streptococcus sobrinus 6715

The complete nucleotide sequences of Streptococcus sobrinus 6715 scrA and scrB, which encode sucrose-specific enzyme II of the phosphoenolpyruvate-dependent phosphotransferase system and sucrose-6-phosphate hydrolase, respectively, have been determined. These two genes were transcribed divergently, and the initiation codons of the two open reading frames were 192 bp apart. The transcriptional initiation sites were determined by primer extension analysis, and the putative promoter regions of these two genes overlapped partially. The gene encoding enzyme IIScr, scrA, contained 1,896 nucleotides, and the molecular mass of the predicted protein was 66,529 Da. The hydropathy plot of the predicted amino acid sequence indicated that enzyme IIScr was a relatively hydrophobic protein. The gene encoding sucrose-6-phosphate hydrolase, scrB, contained 1,437 nucleotides. The molecular mass of the predicted protein was 54,501 Da, and the encoded enzyme was hydrophilic. The predicted amino acid sequences of the two open reading frames exhibited approximately 45 and 70% identity with those encoded by scrA and scrB, respectively, from Streptococcus mutans GS5. Homology also was observed between the N-terminal region of the S. sobrinus 6715 enzyme IIScr and other enzyme IIs specific for the glucopyranoside molecule, all of which generate glucopyranoside-6-phosphate during translocation and phosphorylation of the respective substrates. The sequence of the C-terminal domain of the S. sobrinus 6715 enzyme IIScr shared significant homology with enzyme IIIGlc from Escherichia coli and Salmonella typhimurium and with the C-terminal domain of enzyme IIBgl from E. coli, indicating that the two functional domains, enzyme IIScr and enzyme IIIScr, were covalently linked as a single polypeptide in S. sobrinus 6715. The deduced amino acid sequence of the gene product of S. sobrinus scrB shared strong homology with sucrase from Bacillus subtilis, Klebsiella pneumoniae, and Vibrio alginolyticus, suggesting conservation based on the physiological roles of these proteins.

An invertase with unusual properties secreted by sucrose-grown cells of Corynebacterium murisepticum

The mode of sucrose utilisation by Corynebacterium murisepticum cells growing on M9 minimal medium supplemented with 0.4% sucrose as the carbon source was studied. It was observed that during growth of this organism, sucrose in the medium is hydrolysed to glucose and fructose, suggesting the formation of an extracellular invertase. Unlike in other microorganisms (e.g. Saccharomyces cerevisiae) the invertase formation is not repressed by the presence of glucose in the medium. The invertase was found to be the only predominant extracellular protein in the culture broth and could be purified in a single step by precipitation at 90% ammonium sulphate saturation. The purified protein had a molecular mass of 70,000 daltons. It not only showed invertase activity, but also a fructosyltransferase activity as it could convert sucrose to beta-1,2-difructose, as well as to glucose and fructose.

Molecular and active-site structure of a Bacillus 1,3-1,4-beta-glucanase

The three-dimensional structure of the hybrid Bacillus 1,3-1,4-beta-glucanase (beta-glucanase; 1,3-1,4-beta-D-glucan 4-glucanohydrolase, lichenase, EC 3.2.1.73) designated H(A16-M) was determined by x-ray crystallography at a resolution of 2.0 A and refined to an R value of 16.4% using stereochemical restraints. The protein molecule consists mainly of two seven-stranded antiparallel beta-pleated sheets arranged atop each other to form a compact, sandwich-like structure. A channel crossing one side of the protein molecule accommodates an inhibitor, 3,4-epoxybutyl beta-D-cellobioside, which binds covalently to the side chain of Glu-105, as seen in a crystal structure analysis at 2.8-A resolution of the protein-inhibitor complex (R = 16.8%). That Glu-105 may be indispensible for enzyme catalysis by H(A16-M) is suggested by site-directed mutagenesis of this residue, which inevitably leads to an inactive enzyme.

Purification and characterization of a new agarase from a marine bacterium, Vibrio sp. strain JT0107

A marine bacterial strain that decomposes the cell walls of some seaweeds, including a Laminaria sp. and Undaria pinnatifida, has been isolated from seawater. This strain has been classified to the genus Vibrio. One of the enzymes which the bacteria secreted into the culture medium was isolated and purified 45-fold from the culture fluid by a combination of ammonium sulfate precipitation and successive rounds of anion-exchange column chromatography. Purified protein migrated as a single band (M(r), 107,000) on sodium dodecyl sulfate-polyacrylamide gels. By amino acid sequence analysis, it was determined that this protein had a single N-terminal sequence that did not exhibit identity with the sequences of other agarases from marine bacteria. This novel enzyme was found to be an endo-type beta-agarase (EC 3.2.1.81) which hydrolyzes the beta-1,4 linkage of agarose to yield neoagarotetraose [O-3,6-anhydro-alpha-L-galactopyranosyl (1-->3)-O-beta-D-galactopyranosyl(1-->4)-O-3,6-anhydro-alpha-L-galactopy ranosyl (1-->3)-D-galactose] and neoagarobiose [O-3,6-anhydro-alpha-L-galactopyranosyl (1-->3)-D-galactose] at a pH of around 8. The optimum temperature was 30 degrees C. This enzyme did not decompose sodium alginate or lambda-, iota-, or kappa-carrageenan. This enzyme may be of practical application in gene technology in the isolation of DNA fragments from agarose gels after electrophoresis.