Solution structure of murine macrophage inflammatory protein-2

The solution structure of murine macrophage inflammatory protein-2 (MIP-2), a heparin-binding chemokine that is secreted in response to inflammatory stimuli, has been determined using two-dimensional homonuclear and heteronuclear NMR spectroscopy. Structure calculations were carried out by means of torsion-angle molecular dynamics using the program X-PLOR. The structure is based on a total of 2390 experimental restraints, comprising 2246 NOE-derived distance restraints, 44 distance restraints for 22 hydrogen bonds, and 100 torsion angle restraints. The structure is well-defined, with the backbone (N, Calpha, C) and heavy atom atomic rms distribution about the mean coordinates for residues 9-69 of the dimer being 0.57 +/- 0.16 A and 0.96 +/- 0.12 A, respectively. The N- and C-terminal residues (1-8 and 70-73, respectively) are disordered. The overall structure of the MIP-2 dimer is similar to that reported previously for the NMR structures of MGSA and IL-8 and consists of a six-stranded antiparallel beta-sheet (residue 25-29, 39-44, and 48-52) packed against two C-terminal antiparallel alpha-helices. A best fit superposition of the NMR structure of MIP-2 on the structures of MGSA, NAP-2, and the NMR and X-ray structures of IL-8 are 1.11, 1.02, 1.27, and 1.19 A, respectively, for the monomers, and 1.28, 1.10, 1.55, and 1.36 A, respectively, for the dimers (IL-8 residues 7-14 and 16-67, NAP-2 residues 25-84). At the tertiary level, the main differences between the MIP-2 solution structure and the IL-8, MGSA, and NAP-2 structures involve the N-terminal loop between residues 9-23 and the loops formed by residues 30-38 and residues 53-58. At the quaternary level, the difference between MIP-2 and IL-8, MGSA, or NAP-2 results from differing interhelical angles and separations.

Long-term cytokine alterations following allogeneic blood transfusion

BACKGROUND

Allogeneic blood transfusion is associated with an increased risk of infection and higher cancer recurrence rates. Previous research has shown that blood transfusion results in multiple immune effects, including cytokine alterations. The purpose of this study was to measure the long term kinetics of splenocyte cytokine production in transfused mice.

METHODS

Balb/c mice received either syngeneic transfusion (Syn-BT) or allogeneic transfusion (Allo-BT) from C3H-HeN mice. Splenocyte production of IL-2, IL-6, IL-10, and IFN-gamma was quantitated by ELISA on post-transfusion days 5, 10, 21, and 30.

RESULTS

Both Allo-BT and Syn-BT produced significant alterations in cytokine production, but Allo-BT produced the most dramatic and enduring effects as summarized: IL-2: Production of IL-2 was suppressed at day 5, (p < 0.0001), but then rose, peaking at day 21, 30% greater than control values (p < 0.05). IL-6: Allo-BT mice showed suppression of IL-6 throughout the study period (p < 0.005 vs controls, each time point). IL-10: A 5-fold increase in IL-10 production was seen at day 5 after Allo-BT (p < 0.0001 vs control). Production of IL-10 was suppressed at days 10 and 21 (p < 0.001), but returned to control levels by day 30, gamma-IFN: At day 5 post Allo-BT, gamma-IFN was 4 x greater than controls (p < 0.0001). Gamma-IFN production was suppressed at day 10, but then rose at days 21 and 30 to nearly 3 x control levels (p < 0.0001).

CONCLUSION

Allo-BT produced multiple cytokine alterations that were of prolonged duration. These results provide a theoretic explanation for the multiple, long-term immunomodulating effects seen in patients who have received transfusions.

Role of the histone deacetylase complex in acute promyelocytic leukaemia

Non-liganded retinoic acid receptors (RARs) repress transcription of target genes by recruiting the histone deacetylase complex through a class of silencing mediators termed SMRT or N-CoR. Mutant forms of RARalpha, created by chromosomal translocations with either the PML (for promyelocytic leukaemia) or the PLZF (for promyelocytic leukaemia zinc finger) locus, are oncogenic and result in human acute promyelocytic leukaemia (APL). PML-RARalpha APL patients achieve complete remission following treatments with pharmacological doses of retinoic acids (RA); in contrast, PLZF-RARalpha patients respond very poorly, if at all. Here we report that the association of these two chimaeric receptors with the histone deacetylase (HDAC) complex helps to determine both the development of APL and the ability of patients to respond to retinoids. Consistent with these observations, inhibitors of histone deacetylase dramatically potentiate retinoid-induced differentiation of RA-sensitive, and restore retinoid responses of RA-resistant, APL cell lines. Our findings suggest that oncogenic RARs mediate leukaemogenesis through aberrant chromatin acetylation, and that pharmacological manipulation of nuclear receptor co-factors may be a useful approach in the treatment of human disease.

Arsenic trioxide as an inducer of apoptosis and loss of PML/RAR alpha protein in acute promyelocytic leukemia cells

BACKGROUND

Retinoids, which are derivatives of vitamin A, induce differentiation of acute promyelocytic leukemia (APL) cells in vitro and in patients. However, APL cells develop resistance to retinoic acid treatment. Arsenic trioxide (As2O3) can induce clinical remission in patients with APL, including those who have relapsed after retinoic acid treatment, by inducing apoptosis (programmed cell death) of the leukemia cells. In this study, we investigated the molecular mechanisms by which As2O3 induces apoptosis in retinoic acid-sensitive NB4 APL cells, in retinoic acid-resistant derivatives of these cells, and in fresh leukemia cells from patients.

METHODS

Apoptosis was assessed by means of DNA fragmentation analyses, TUNEL assays (i.e., deoxyuridine triphosphate labeling of DNA nicks with terminal deoxynucleotidyl transferase), and flow cytometry. Expression of the PML/RAR alpha fusion protein in leukemia cells was assessed by means of western blotting, ligand binding, and immunohistochemistry. Northern blotting and ribonuclease protection assays were used to evaluate changes in gene expression in response to retinoic acid and As2O3 treatment.

RESULTS AND CONCLUSIONS

As2O3 induces apoptosis without differentiation in retinoic acid-sensitive and retinoic acid-resistant APL cells at concentrations that are achievable in patients. As2O3 induces loss of the PML/RAR alpha fusion protein in NB4 cells, in retinoic-acid resistant cells derived from them, in fresh APL cells from patients, and in non-APL cells transfected to express this protein. As2O3 and retinoic acid induce different patterns of gene regulation, and they inhibit the phenotypes induced by each other. Understanding the molecular basis of these differences in the effects of As2O3 and retinoic acid may guide the clinical use of arsenic compounds and provide insights into the management of leukemias that do not respond to retinoic acid.

[Study of the inclusion compound of rutin with beta-cyclodextrin]

In order to improve the solubility of Rutin in aqueous solution and the stability, the inclusion compound of Rutin with beta-CD was manufacted by saturated aqueous solution method. The formation of the inclusion compound was confirmed by IR spectroscopy and differential scauning calorimetry. The content of Rutin in inclusion compound was determined by UV. The results indicated that the inclusion compound of Rutin with beta-CD was formed. Quantitative analysis demmonstrated that the molecular ratio of Rutin to beta-CD in the complex was 1:1 with the inclusion constant of 283.79 L/mol at 30 degrees C. The dissolubility of Rutin in water has added to 643.19 mg/L (20 degrees C).

The 1997 Lindberg Award. Effects of burn injury on bone and growth in a mouse model

Bone growth and remodeling are inhibited by severe burns in adult and pediatric patients, resulting in alterations in linear growth, bone mass, osteoporosis, and increased risk for pathologic fractures. This study of a mouse model of burn injury showed skeletal changes similar to those reported in patients with burn injuries. Baseline, control, sham, and burned mice were injected with fluorescent markers calcein and tetracycline for histomorphometric analysis. Total femur dry and ash weights and total calcium content were significantly lower 10 days after burn injury compared with sham and control animals. There also were decreases in the percentage of fluorochrome-labeled bone surfaces and bone formation rates in the burn-injured mice compared with control and sham mice; however, there were no differences in the mineral apposition rates. This model now provides an opportunity to examine cellular and molecular mechanisms contributing to skeletal pathology in a well-defined burn injury model.

Biochemical and molecular characterization of PepR, a dipeptidase, from Lactobacillus helveticus CNRZ32

A dipeptidase with prolinase activity from Lactobacillus helveticus CNRZ32, which was designated PepR, was purified to gel electrophoretic homogeneity and characterized. The NH2-terminal amino acid sequence of the purified protein had 96% identity to the deduced NH2-terminal amino acid sequence of the pepR gene, which was previously designated pepPN, from L. helveticus CNRZ32. The purified enzyme hydrolyzed Pro-Met, Thr-Leu, and Ser-Phe as well as dipeptides containing neutral, nonpolar amino acid residues at the amino terminus. Purified PepR was determined to have a molecular mass of 125 kDa with subunits of 33 kDa. The isoelectric point of the enzyme was determined to be 4.5. The optimal reaction conditions, as determined with Pro-Leu as substrate, were pH 6.0 to 6.5 and 45 to 50 degrees C. The purified PepR had a Km of 4.9 to 5.2 mM and a Vmax of 260 to 270 mumol of protein per min/mg at pH 6.5 and 37 degrees C. The activity of purified PepR was inhibited by Zn2+ but not by other cations or cysteine, serine, aspartic, or metal-containing protease inhibitors or reducing agents. Results obtained by site-directed mutagenesis indicated that PepR is a serine-dependent protease. Gene replacement was employed to construct a PepR-deficient derivative of CNRZ32. This mutant did not differ from the wild-type strain in its ability to acidify milk. However, the PepR-deficient construct was determined to have reduced dipeptidase activity compared to the wild-type strain with all dipeptide substrates examined.

A retinoid-resistant acute promyelocytic leukemia subclone expresses a dominant negative PML-RAR alpha mutation

The unique t(15;17) of acute promyelocytic leukemia (APL) fuses the PML gene with the retinoic acid receptor alpha (RAR alpha) gene. Although retinoic acid (RA) inhibits cell growth and induces differentiation in human APL cells, resistance to RA develops both in vitro and in patients. We have developed RA-resistant subclones of the human APL cell line, NB4, whose nuclear extracts display altered RA binding. In the RA-resistant subclone, R4, we find an absence of ligand binding of PML-RAR alpha associated with a point mutation changing a leucine to proline in the ligand-binding domain of the fusion PML-RAR alpha protein. In contrast to mutations in RAR alpha found in retinoid-resistant HL60 cells, in this NB4 subclone, the coexpressed RAR alpha remains wild-type. In vitro expression of a cloned PML-RAR alpha with the observed mutation in R4 confirms that this amino acid change causes the loss of ligand binding, but the mutant PML-RAR alpha protein retains the ability to heterodimerize with RXR alpha and thus to bind to retinoid response elements (RAREs). This leads to a dominant negative block of transcription from RAREs that is dose-dependent and not relieved by RA. An unrearranged RAR alpha engineered with this mutation also lost ligand binding and inhibited transcription in a dominant negative manner. We then found that the mutant PML-RAR alpha selectively alters regulation of gene expression in the R4 cell line. R4 cells have lost retinoid-regulation of RXR alpha and RAR beta and the RA-induced loss of PML-RAR alpha protein seen in NB4 cells, but retain retinoid-induction of CD18 and CD38. Thus, the R4 cell line provides data supporting the presence of an RAR alpha-mediated pathway that is independent from gene expression induced or repressed by PML-RAR alpha. The high level of retinoid resistance in vitro and in vivo of cells from some relapsed APL patients suggests similar molecular changes may occur clinically.

The effects of imidazole binding on the conformation of cytochrome c

Many individual protons exhibit different chemical shifts in Im-cyt c and cyt c, reflecting diamagnetic shift effects as a result of structure change, and in addition contact and pseudocontact shifts that occur only in the paramagnetic oxidized form. To estimate the chemical shift differences caused by structure change, we removed the pseudocontact shift contribution. The anisotropy and direction of the magnetic susceptibility anisotropy tensor were determined. There was evidence for conformational changes induced by the breakage of Fe-S bond. It was concluded that the Im-cyt c had undergone a rearrangement of several regions forming the heme pocket of the protein. The hydrogen-bond network in the heme cavity was affected by the substitution.

Secondary structure of T4 gene 33 protein. Fourier transform infrared and circular dichroic spectroscopic studies

The secondary structure of bacteriophage T4 gene 33 protein (gp33) has been quantitatively examined by using Fourier transform infrared (FT-IR) and circular dichroism (CD) spectroscopy. Resolution enhancement techniques, including Fourier deconvolution and derivative spectroscopy were used to quantitate the spectral information from the amide I bands. The relative areas of these component bands indicate 21% alpha-helix, 25% beta-sheet, 34% turn, 12% random coil and 8% other undefined structures in gp33. An analysis of the CD spectrum of gp33 at the same pH and temperature revealed 19% alpha-helix, 25% beta-sheet, 13% turn and 43% random coil structures. The possible reasons for the discrepancies in estimates of the contributions to the secondary structure from turns and random coils are discussed.

Sequence requirements of the HIV-1 protease flap region determined by saturation mutagenesis and kinetic analysis of flap mutants

The retroviral proteases (PRs) have a structural feature called the flap, which consists of a short anti-parallel beta-sheet with a turn. The flap extends over the substrate binding cleft and must be flexible to allow entry and exit of the polypeptide substrates and products. We analyzed the sequence requirements of the amino acids within the flap region (positions 46-56) of the HIV-1 PR. The phenotypes of 131 substitution mutants were determined using a bacterial expression system. Four of the mutant PRs with mutations in different regions of the flap were selected for kinetic analysis. Our phenotypic analysis, considered in the context of published structures of the HIV-1 PR with a bound substrate analogs, shows that: (i) Met-46 and Phe-53 participate in hydrophobic interactions on the solvent-exposed face of the flap; (ii) Ile-47, Ile-54, and Val-56 participate in hydrophobic interactions on the inner face of the flap; (iii) Ile-50 has hydrophobic interactions at the distance of both the delta and gamma carbons; (iv) the three glycine residues in the beta-turn of the flap are virtually intolerant of substitutions. Among these mutant PRs, we have identified changes in both kcat and Km. These results establish the nature of the side chain requirements at each position in the flap and document a role for the flap in both substrate binding and catalysis.

Characterization of HMBP-2, a DNA-Binding Protein That Binds to HIV-1 LTR When only One of the Three Sp1 Sites Is Methylated

HIV-1 methylation binding protein-1 (HMBP-1) (formerly called HMBP) is a protein found in human cell nuclei that binds with enhanced affinity to a fragment of the HIV-1 long terminal repeat sequence (LTR) containing three Sp1 sites when all three sites are methylated. HMBP-2 is another protein present in the nuclei of human T helper lymphocytes and HeLa cells that binds to the HIV-1 LTR. HMBP-2 binds preferentially to the same region of the HIV-1 LTR as does HMBP-1, but HMBP-2 binds best when only one of the three Sp1 sites is methylated. HMBP-2 can be separated from HMBP-1 chromatographically, and dimethyl sulftate (DMS) methylation interference analysis indicates that their binding sites are not identical. HMBP-2 represents a novel protein factor capable of binding to a partially methylated region of the HIV-1 LTR. Copyright 1997 S. Karger AG, Basel

Structural studies of imidazole-cytochrome c: resonance assignments and structural comparison with cytochrome c

Two-dimensional nuclear magnetic resonance spectroscopy (2D NMR) was used to obtain extensive proton resonance assignments of Im-cyt c complex which is a possible analog of a late folding intermediate of cytochrome c. Assignments were made nearly completely for the main-chain and the side-chain protons (all except Gly29). As starting points for the assignment of the Im-cyt c, a limited set of protons was initially assigned by use of 2D NMR magnetization transfer methods to correlated resonances in the Im-cyt c with assigned resonances in the native cyt c. The subsequent search focused on recognition of main-chain NOE connectivity patterns, with use of previously assigned residues to place NOE-connected segments within the amino acid sequence. The observed patterns of main-chain NOEs provided some structural information and suggested potentially significant differences between Im-cyt c and the native cyt c. Differences in NOEs involving side-chain protons were reported and analyzed. There was evidence for conformational changes induced by the breakage of Fe-S bond. It was concluded that the Im-cyt c had undergone a rearrangement of several regions forming the heme pocket of the protein. The structural understanding of these effects of the mutation may be essential to elucidate the changes in function and kinetic mechanism of cyt c folding.

2D-NMR studies of the effects of axial substitution on two helices in horse cytochrome c

The sequential amino acids from Gly-1 to Cys-14 in the N-terminal segment and from Lys-88 to Glu-104 in the C-terminal segment of cytochrome c-imidazole complex (Im-cyt c) have been studied by two-dimensional nuclear magnetic resonance techniques. Resonance assignments for the main-chain and side-chain protons are reported. Qualitative interpretation of nuclear Overhauser enhancement data allows the secondary structure of the two segments to be described, which indicate the patterns of NOEs found are consistent with an alpha-helix between Val-3 and Cys-14 in the N-terminus, and between Lys-88 and Asn-103 in the C-terminus. Two alpha-helices are found to be maintained. Comparison of the long-range NOEs of Im-cyt c relative to the crystal structure of native cytochrome c reveals apparent conformational changes of some side-chains especially those close to heme pocket within the N- and C-terminal helices resulting from the binding of imidazole to iron by displacing native Met-80 side-chain. The explanation for ligand-induced changes within the N- and C-helices is therefore suggested.

Microcapsules obtained from complex coacervation of collagen and chondroitin sulfate

Microcapsules composed of collagen and chondroitin sulfate were obtained by complex coacervation and characterized by DSC, optical microscopy, SEM, and UV-Vis spectroscopy. Composition of the microcapsules could be adjusted by the feed ratio and the pH of the solution. Prepared under low temperature and aqueous solution, the process is most suitable for encapsulating delicate bioactive agents. Albumin as a model protein was encapsulated with a loading level of up to 95% by weight. Degradation rate of the microcapsules decreased with the concentration of the crosslinking agent glutaraldehyde and increased with the bacterial collagenase level. Correspondingly the release of albumin could also be varied by the cross-linking degree of the microcapsules.

Effects of axial ligand replacement on the redox potential of cytochrome c

The formal potentials (E0') and electron transfer numbers (n) of imidazole (Im), 1-methylimidazole (1-MeIm), and 1-ethylimidazole (1-EtIm) complexes of cytochrome c have been determined for the first time using optically transparent thin-layer spectroelectrochemistry. In comparing these results with the E0' value of the cytochrome c, their potentials at infinite dilution have been calculated, which indicate that axial replacement of methionine-80 by Im, 1-MeIm, and 1-EtIm gives rise to 426, 359, and 327 mV negative shifts relative to that of native cytochrome c, respectively. Thereby, the origins of the effects of axial substitution on redox potential are discussed.

Binding of 1-methylimidazole to cytochrome c: kinetic analysis and resonance assignments by two-dimensional NMR

The binding of 1-methylimidazole to the heme iron by displacing Met-80 of cytochrome c has been studied by two-dimensional (2D) exchange spectroscopy. Two components of cytochrome c ligated by 1-methylimidazole (1-MeIm-cyt c) are first identified, which are related to the sterically hindered orientation of 1-methylimidazole by the heme pocket. Based on a matrix formalism, the kinetic parameters are calculated from the 2D peak amplitudes. With the known resonance assignments of cytochrome c, some hyperfine shifted resonances arising from heme peripheral protons and two axial ligands, and some side-chain resonances of the aliphatic and aromatic protons of 1-MeIm-cyt c have been straightforwardly assigned, which provide a clue to ligand-induced electronic and molecular structural changes of the protein.

A side chain at position 48 of the human immunodeficiency virus type-1 protease flap provides an additional specificity determinant

Substitution of glycine with glutamic acid at position 48 of the human immunodeficiency virus protease resulted in an enzyme with reduced activity on one of the protease processing sites in the viral Pol polyprotein precursor. Cleavage at this site was restored by a second-site substitution in the substrate replacing an aspartic acid with either glycine or asparagine. These results suggest that the glutamic acid side chain in the mutant protease has an unfavorable charge-charge interaction with this position in the substrate. Cleavage of a processing site in the viral Gag polyprotein precursor with the mutant enzyme was enhanced, and this enhancement was dependent on the presence of an arginine residue in the substrate, again suggesting a charge-charge interaction. The potential for such interactions was confirmed using molecular modeling. The effect of the position 48 substitution was attributed to a 10-fold increase in Km for the processing site in Pol. These results indicate that the addition of a side chain at position 48 can alter the specificity of the HIV-1 protease to substrate in a sequence specific manner and that compensatory changes can be made in the substrate.

Purification and Characterization of the (alpha)-Glucuronidase from Thermoanaerobacterium sp. Strain JW/SL-YS485, an Important Enzyme for the Utilization of Substituted Xylans

A cell-associated (alpha)-glucuronidase was purified to gel electrophoretic homogeneity from the thermophilic anaerobic bacterium Thermoanaerobacterium sp. strain JW/SL-YS485. This enzyme had a pI of 4.65, a molecular weight of 130,000, and two subunits; the molecular weight of each subunit was 74,000. The enzyme exhibited the highest level of activity at pH 5.4 and 60(deg)C, as determined by a 5-min assay. The K(infm) and k(infcat) values of the enzyme for 4-methylglucuronosyl xylobiose were 0.76 mM and 1,083 IU/(mu)mol, respectively. The Arrhenius energy was 26.4 kJ/mol. The specific activities of the enzyme with 4-O-methylglucuronosyl xylobiose, 4-O-methylglucuronosyl xylotriose, and 4-O-methylglucuronosyl xylotetraose were 8.4, 4.8, and 3.9 IU/mg, respectively. The purified (alpha)-glucuronidase and a (beta)-xylosidase purified from the same organism interacted synergistically to hydrolyze 4-methylglucuronosyl xylotetraose.

Purification and characterization of two thermostable acetyl xylan esterases from Thermoanaerobacterium sp. strain JW/SL-YS485

Two acetyl esterases (EC 3.1.1.6) were purified to gel electrophoretic homogeneity from Thermoanaerobacterium sp. strain JW/SL-YS485, an anaerobic, thermophilic endospore former which is able to utilize various substituted xylans for growth. Both enzymes released acetic acid from chemically acetylated larch xylan. Acetyl xylan esterases I and II had molecular masses of 195 and 106 kDa, respectively, with subunits of 32 kDa (esterase I) and 26 kDa (esterase II). The isoelectric points were 4.2 and 4.3, respectively. As determined by a 2-min assay with 4-methylumbelliferyl acetate as the substrate, the optimal activity of acetyl xylan esterases I and II occurred at pH 7.0 and 80 degrees C and at pH 7.5 and 84 degrees C, respectively. Km values of 0.45 and 0.52 mM 4-methylumbelliferyl acetate were observed for acetyl xylan esterases I and II, respectively. At pH 7.0, the temperatures for the 1-h half-lives for acetyl xylan esterases I and II were 75 degrees and slightly above 100 degrees C, respectively.

A possible vulnerability locus for bipolar affective disorder on chromosome 21q22.3

In a preliminary genome scan of 47 bipolar disorder families, we detected in one family a lod score of 3.41 at the PFKL locus on chromosome 21q22.3. The lod score is robust to marker allele frequencies, phenocopy rates and age-dependent penetrance, and remains strongly positive with changes in affection status. Fourteen other markers in 21q22.3 were tested on this family, with largely positive lod scores. Five of the other 46 families also show positive, but modest lod scores with PFKL. When all 47 families are analysed together, there is little support for linkage to PFKL under homogeneity or heterogeneity using lod score analysis, but the model-free affected-pedigree-member method yields statistically significant results (p < 0.0003). Our results are consistent with the presence of a gene in 21q22.3 predisposing at least one family to bipolar disorder.

A nuclear protein with enhanced binding to methylated Sp1 sites in the AIDS virus promoter

We report here the discovery of HMBP, a protein in nuclei of human T-helper lymphocytes and other human cell types, which binds with enhanced affinity to a promoter element in the HIV-1 long terminal repeat when that element is methylated at CpGs, the target site of the human DNA methyltransferase. This promoter element contains three (degenerate) binding sites for Sp1, a general activator of transcription. Gel shift assays and footprinting experiments indicate that HMBP binding overlaps two of these methylated Sp1 sites. Although HMBP binds these methylated Sp1 sites, it does not bind consensus Sp1 sites. Competition studies, differences in binding site specificities, binding conditions, and, in some cases, chromatographic separation further distinguish HMBP from Sp1 and from each of four previously identified methylated-DNA binding proteins. HMBP binds hemimethylated DNA in a strand dependent manner. These binding characteristics suggest that HMBP may recognize newly replicated DNA and thereby play a role in differentiation. If HMBP is able to compete with Sp1 for binding at methylated, non-consensus Sp1 sites in vivo and repress transcription, it may play a role in AIDS latency.

Purification and characterization of a thermostable beta-xylosidase from Thermoanaerobacter ethanolicus

A highly thermostable beta-xylosidase, exhibiting similarly high activities for arylxylose and arylarabinose, was purified (72-fold) to gel electrophoretic homogeneity from the ethanologenic thermophilic anaerobe Thermoanaerobacter ethanolicus. The isoelectric point is pH 4.6; the apparent molecular weight is around 165,000 for the native enzyme (gel filtration and gradient polyacrylamide gel electrophoresis) and 85,000 for the two subunits (sodium dodecyl sulfate-polyacrylamide gel electrophoresis). The enzyme exhibited the highest affinity towards p-NO2-phenyl xyloside (pNPX) (substrate concentration for half-maximal activity = 0.018 mM at 82 degrees C and pH 5.0) but the highest specific activity with p-NO2-phenylarabinofuranoside. T(opt), 5 min, the temperature for the maximum initial activity in a 5-min assay of the purified enzyme, was observed around pH 5.9 and 93 degrees C; however at 65 and 82 degrees C, the pH optimum was 5.0 to 5.2, and at this pH the maximal initial activity was observed at 82 degrees C (pH 5.0 to 5.5). The pH curves and temperature curves for arylxylosides as substrates differed significantly from those for arylarabinosides as substrates. An incubation for 3 h at 82 degrees C in the absence of substrate reduced the activity to around 75%. At 86 degrees C the half-life was around 15 min. With pNPX as the substrate, an Arrhenius energy of 69 kJ/mol was determined. The N-terminal sequence did not reveal a high similarity to those from other published enzyme sequences.