RESUMO
A glucuronan lyase extracted from Sinorhizobium meliloti strain M5N1CS was purified to homogeneity by anion-exchange chromatography. The purified enzyme corresponds to a monomer with a molecular mass of 20 kDa and a pI of 4.9. A specific activity was found only for polyglucuronates leading to the production of 4,5-unsaturated oligoglucuronates. The enzyme activity was optimal at pH 6.5 and 50 degrees C. Zn(2+), Cu(2+), and Hg(2+) (1 mM) inhibited the enzyme activity. No homology of the enzyme N-terminal amino acid sequence was found with any of the previously published protein sequences. This enzyme purified from S. meliloti strain M5N1CS corresponding to a new lyase was classified as an endopolyglucuronate lyase.
Assuntos
Polissacarídeo-Liases/isolamento & purificação , Polissacarídeo-Liases/metabolismo , Sinorhizobium meliloti/enzimologia , Sequência de Aminoácidos , Dados de Sequência Molecular , Polissacarídeo-Liases/química , Sinorhizobium meliloti/crescimento & desenvolvimento , Especificidade por SubstratoRESUMO
Two Pseudomonas aeruginosa alginates were lysed by an overexpressed polymannuronate lyase AlxMB (only acting on two or more consecutive, nonacetylated mannuronate units) to prepare either mannuronate blocks (poly-M blocks) with dp approximately 30, or strictly alternating sequences of mannuronic and guluronic acid (poly-MG blocks) with dp > 20. The poly-M blocks were obtained by lysis of a P. aeruginosa polymannuronate that has 50% O-acetylation at C-2 and C-3. The poly-MG blocks were obtained from a P. aeruginosa alginate that contained both mannuronate and guluronate residues. The polysaccharide was first deacetylated and then treated with the lyase to excise the mannuronate units from the alternating-MG blocks. Both types of blocks should have potent biological effects and should provide useful specific substrates for characterisation of other alginate lyases.
Assuntos
Alginatos/metabolismo , Polissacarídeo-Liases/metabolismo , Pseudomonas aeruginosa/química , Ácido Glucurônico , Ácidos Hexurônicos , Ressonância Magnética Nuclear BiomolecularRESUMO
Structural studies were performed in two atypical polysaccharides, PS-1 and PS-2 isolated from the broth of a Tn5 mutant strain of Xanthomonas campestris. Sugar composition, methylation and nuclear magnetic resonance analyses were determined. PS-1 is composed by repeating trisaccharide units containing D-glucose, D-mannose and having the structure. carbohydrate sequence [see text]. Preliminary studies on the PS-2 show a polymer composed in a large extent of rhamnose. Unexpectedly, this polysaccharide is soluble in alcoholic solutions.
Assuntos
Celulose/química , Manose/metabolismo , Xanthomonas campestris/metabolismo , Sequência de Carboidratos , Celulose/biossíntese , Celulose/isolamento & purificação , Celulose/metabolismo , Metilação , Dados de Sequência Molecular , Mutação , Polissacarídeos/biossíntese , Polissacarídeos/isolamento & purificação , Xanthomonas campestris/genéticaRESUMO
Lysis of alginates and of their saturated and unsaturated fragments was monitored by 1H NMR spectroscopy. AlxM(B) alginate lyase performs beta-elimination on the mannuronic acid (M) residues. It does not cleave the guluronic acid (G) sequences, nor the M-G or the G-M diads. In consequence, it is a true mannuronate lyase. The end product of the reaction is O-(4-deoxy-alpha-L-ery-thro-hex-4-enopyranosyl-uronic acid)-(1->(4)-O-(beta-D-mannopyranosyluronic acid)-(1->4)-O-beta-D-mannpyranuronic acid. Viscosity measurements made during degradation of a polymannuronate alginate showed that AlxM(B) behaves as an endo-enzyme. HPLC analysis of the degradation products of oligomannuronates and oligoalginates suggested that the beta-elimination requires the interaction of the enzyme with at least three sequential mannuronic acid residues. The catalytic site may possess 5 sub-sites and accommodate pentamers with different M/G ratio. Kinetic measurements showed that the specificity constant Vm/Km increased with the number of mannuronic acid residues. AlxM(B) may be reversibly inhibited by heteropolymeric blocks in a competitive manner.
Assuntos
Polissacarídeo-Liases/metabolismo , Alginatos/metabolismo , Cinética , Ressonância Magnética Nuclear Biomolecular , Proteínas Recombinantes/metabolismo , Especificidade por SubstratoRESUMO
The extracellular polysaccharide produced by Lactobacillus rhamnosus strain C83 was found to be composed of D-glucose and D-galactose in a molar ratio of 2:3. The primary structure of the polysaccharide was shown by sugar analysis, methylation analysis, FABMS, partial acid hydrolysis and nuclear magnetic resonance (NMR) spectroscopy to consist of a pentasaccharide repeating unit having the following structure: -->3)-alpha-D-Glcp-(1-->2)-beta-D-Galf-(1-->6)-alpha-D-Galp-(1-->6 )-alpha-D -Glcp-(1-->3)-beta-D-Galf-(1-->
Assuntos
Lactobacillus/química , Polissacarídeos/química , Sequência de Carboidratos , Cromatografia Gasosa-Espectrometria de Massas , Espectroscopia de Ressonância Magnética , Metilação , Dados de Sequência Molecular , Estrutura Molecular , Polissacarídeos/isolamento & purificaçãoRESUMO
The chromatographic behaviour of various saturated and unsaturated oligouronates obtained by acid or enzymatic degradation of homopolymeric blocks of alginates was investigated by isocratic anion exchange liquid chromatography. This approach was then applied to the determination of the catalytic properties of Haliotis tuberculata alginate lyase. This enzyme presents a high affinity for poly-beta-D-mannuronate blocks, leading to the release of O-(4-deoxy-alpha-L-erythro-hex-4-enopyranosyluronic acid)-(1-->4)-O-(beta-D-mannopyranosyluronic acid)-(1-->4)-O-beta-D-mannopyranuronic acid as the main end reaction product. Kinetic analysis with oligomannuronates of various sizes indicate that the catalytic site of Haliotis tuberculata lyase (abalone) best accommodates an oligomannuronate pentamer. The abalone lyase, however, is also capable of cleaving the G-M linkages of alginate heteropolymeric sequences. In contrast, it does not degrade the G-G nor the M-G diads. This lyase should therefore be referred to as a mannuronate beta-eliminase, indicating that the enzyme performs beta-elimination on mannuronate residues only, from both the M-M and G-M diads of alginates.
Assuntos
Alginatos/metabolismo , Moluscos/enzimologia , Oligossacarídeos/química , Polissacarídeo-Liases/metabolismo , Ácidos Urônicos/química , Alginatos/isolamento & purificação , Animais , Sítios de Ligação , Cromatografia em Gel , Cromatografia Líquida de Alta Pressão , Ácidos Hexurônicos/química , Espectroscopia de Ressonância Magnética , Manose/análogos & derivados , Oligossacarídeos/análise , Oligossacarídeos/metabolismo , Concentração Osmolar , Ácidos Urônicos/análiseRESUMO
During fermentation, the mutant strain Rhizobium meliloti M5N1CS, which induces nodule formation on alfalfa roots, produces a partially acetylated (1-->4)-beta-D-glucuronan. In addition to this exopolysaccharide of high molecular weight, the mutant strain produces oligoglucoronates and cyclic (1-->2)-beta-D-glucans with degrees of polymerization from 17 to 30. Under the conditions applied, magnesium has no effect on cyclic glucan production by the mutant strain, but the succinoglycan production by the wild-type strain Rhizobium meliloti M5N1 increases.
Assuntos
Glucanos/metabolismo , Polissacarídeos Bacterianos/biossíntese , Polissacarídeos Bacterianos/metabolismo , Polissacarídeos/biossíntese , Sinorhizobium meliloti/metabolismo , beta-Glucanas , Acetilação , Cromatografia Líquida de Alta Pressão , Meios de Cultura/farmacologia , Fermentação , Magnésio/farmacologia , Espectroscopia de Ressonância Magnética , Polímeros , Sinorhizobium meliloti/classificação , Sinorhizobium meliloti/efeitos dos fármacos , Especificidade da EspécieRESUMO
The mutant Rhizobium meliloti M5N1CS (NCIMB 40472) produced a partially acetylated (1-->4)-beta-D-glucuronan during fermentation. The polysaccharide (EPS) extracted from broth during fermentation by microfiltration and ultrafiltration (using a 100 kDa cut-off membrane) was characterized by size exclusion chromatography. The weight-average molecular weight (Mw) of the EPS decreased from 7.5 x 10(5) to 5 x 10(5) between 27 and 75 h of fermentation. When MgSO4.7H2O (0.8 gl-1 per day) was present in the medium during the same period, the Mw of the EPS decreased to 1.5 x 10(5). Since EPS degradation was detected after microfiltration of the fermentation medium supplemented with magnesium, the Mw decrease of the EPS extracted during fermentation may be explained by enzymic degradation of the polymer activated by Mg2+ ions.
Assuntos
Proteínas de Bactérias/metabolismo , Glucuronidase/metabolismo , Magnésio/farmacologia , Polissacarídeos/química , Sinorhizobium meliloti/metabolismo , Fenômenos Químicos , Físico-Química , Cromatografia em Gel , Fermentação , Espectroscopia de Ressonância Magnética , Peso Molecular , Polissacarídeos/biossíntese , Polissacarídeos/metabolismo , Sinorhizobium meliloti/genética , Ultrafiltração , ViscosidadeRESUMO
The mutant strain M5N1 C.S. (NCIMB 40472) of Rhizobium meliloti M5N1 is able to produce during fermentation a partially acetylated extracellular (1-->4)-beta-D-glucuronan. At low concentration (1 g.l-1), in the presence of monovalent cations, this new glucuronate behaves as a thickening agent, whereas at higher concentration a thermoreversible gel is obtained. With such divalent cations as Ca2+, a thermally stable gel can be formed.