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PubMed1993

An overview of the recent advances on the physiology and molecular biology of lignin peroxidases of Phanerochaete chrysosporium.

The lignin-degrading white-rot fungus Phanerochaete chrysosporium produces two families of extracellular peroxidases designated lignin peroxidases (LIPs) and manganese-dependent peroxidases (MNPs) which are components of the lignin degradation system of this organism. The number and types of LIP and MNP isozymes produced vary dramatically in response to changes in culture conditions. Protease-mediated degradation of LIPs was shown to be the major cause for the decay of LIP activity in idiophasic cultures of P. chrysosporium. Use of biochemical mutants has not only yielded information on the relative importance of LIPs and MNPs in lignin degradation but has given us insights into the regulation of production of LIPs and MNPs. The genes encoding the major LIPs have been cloned and sequenced and were shown to have a high degree of homology to each other. Karyotyping studies indicated that heterokaryotic strains contain ten chromosomes and that the LIP genes are distributed on at least two chromosomes.

Amino Acid Sequence↗
PubMed1984

Biochemistry of the oxidation of lignin by Phanerochaete chrysosporium.

The objective of this research was to identify the biochemical agents responsible for the oxidative degradation of lignin by the white-rot fungus Phanerochaete chrysosporium. We examined the hypothesis that activated oxygen species are involved, and we also sought the agent in ligninolytic cultures responsible for a specific oxidative degradative reaction in substructure model compounds. Results of studies of the production of activated oxygen species by cultures, of the effect of their removal on ligninolytic activity, and of their action on substructure model compounds support a role for hydrogen peroxide (H(2)O(2)) and possibly superoxide (O(2)(*)(-)) in lignin degradation. Involvement of hydroxyl radical (*OH) or singlet oxygen (1O(2)) is not supported by our data. The actual biochemical agent responsible for one important oxidative C-C bond cleavage reaction in non-phenolic lignin substructure model compounds, and in lignin itself, was found to be an enzyme. The enzyme is extracellular, has a molecular weight of 42,000 daltons, is azide-sensitive, and requires H(2)O(2) for activity.

Journal Article↗
PubMed1995

Metallophthalocyanines as possible lignin peroxidase models.

Several metalloporphyrins, particularly highly chlorinated water soluble meso-tetraphenylporphyrins, have been shown to be good biomimetics of the lignin peroxidases which degrade lignin in vivo. Metal complexes of the water soluble phthalocyaninetetrasulfonic acid have been examined as catalysts for the oxidation of lignin since the phthalocyanines are readily available and inexpensive. The copper(II), nickel(II) and cobalt(II) complexes showed little catalytic activity towards the oxidation of veratryl alcohol (a substrate of the lignin peroxidases). The iron(III) and manganese(III) complexes on the other hand were able to catalyze the oxidation of veratryl alcohol, 4-ethoxy-3-methoxyphenyl-glycerol-beta-guaiacyl ether (a beta-O-4-dimer) and 1-(4-ethoxy-3-methoxy)-2-(4-methoxyphenyl)-1,3-propanediol (a beta-1 dimer). These catalysts are, however, much less stable than the halogenated meso-tetraphenylporphyrins and this lower stability, which is dependent upon pH and the oxidant, limits their use as catalysts.

Benzyl Alcohols↗
PubMed1988

Structure and regulation of a lignin peroxidase gene from Phanerochaete chrysosporium.

We have been investigating the structure and regulation of the lignin peroxidase genes from Phanerochaete chrysosporium. The gene for lignin peroxidase isozyme H8 was isolated and sequenced. The gene is split into nine exons and eight introns. The introns have consensus sequences both at the splice junctions and at an internal element which may be involved in the splicing mechanism. The promoter contains the eukaryotic consensus elements: a TATA box at -78 and a ACAAT box at -106. Transcription initiates downstream from these sequences as verified by S1 nuclease mapping. Induction of the genes for the lignin peroxidase isozymes during growth under nitrogen and under carbon limitation were compared by analyses of RNA and protein. The results indicate that the lignin peroxidase isozymes are differentially regulated in response to environmental stress.

Base Sequence↗
PubMed2004

Heterologous expression of lignin peroxidase of Phanerochaete chrysosporium in Pichia methanolica.

The cDNA encoding for lignin peroxidase of Phanerochaete chrysosporium was expressed in the Pichia methanolica under the control of the alcohol oxidase (AUG1) promoter which was followed by either the lignin peroxidase leader peptide of Phanerochaete chrysosporium or the Saccharomyces cerevisiae alpha-factor signal peptide. Both peptides efficiently directed the secretion of lignin peroxidase from the recombinant yeast cell. The extracellular lignin peroxidase activity in two recombinants was 932 U l(-1) and 1933 U l(-1). The purity of the recombinant product was confirmed by SDS-PAGE.

Cloning, Molecular↗
PubMed2001

Water sorption-desorption in conifer cuticles: The role of lignin.

Current information on the type and amount of biopolymers present in the epidermis of conifer species is still insufficient. This work presents the detailed morphology and chemical composition of Araucaria bidwillii cuticle after selective treatments to remove the different types of biopolymers. After removal of the waxes, cutin and polar hydrolyzable components, a lignin-like fraction, which makes up 25% of the initial cuticle weight, was identified by GC-MS and infrared spectroscopy. The isolated lignin is of G type, mainly formed by guaiacyl units. This composition indicates that the conifer cuticle investigated here has similar composition to other conifer-isolated cuticles. Water sorption and desorption by the isolated cuticle and the different cuticle fractions, including lignin, were studied. The analysis of the isotherms, following distinct physicochemical models, gave useful information on the structural and physiological role of the different biopolymers present in the cuticle. Lignin fraction showed both a high water sorption and capability of retaining it in comparision to other cuticle components. Hysteresis effect on water sorption-desorption cycle and water cluster formations has also been studied, and their physiological role discussed.

Journal Article↗
PubMed1990

Comparison of lignin peroxidase, horseradish peroxidase and laccase in the oxidation of methoxybenzenes.

Lignin peroxidase oxidizes non-phenolic substrates by one electron to give aryl-cation-radical intermediates, which react further to give a variety of products. The present study investigated the possibility that other peroxidative and oxidative enzymes known to catalyse one-electron oxidations may also oxidize non-phenolics to cation-radical intermediates and that this ability is related to the redox potential of the substrate. Lignin peroxidase from the fungus Phanerochaete chrysosporium, horseradish peroxidase (HRP) and laccase from the fungus Trametes versicolor were chosen for investigation with methoxybenzenes as a homologous series of substrates. The twelve methoxybenzene congeners have known half-wave potentials that differ by as much as approximately 1 V. Lignin peroxidase oxidized the ten with the lowest half-wave potentials, whereas HRP oxidized the four lowest and laccase oxidized only 1,2,4,5-tetramethoxybenzene, the lowest. E.s.r. spectroscopy showed that this congener is oxidized to its cation radical by all three enzymes. Oxidation in each case gave the same products: 2,5-dimethoxy-p-benzoquinone and 4,5-dimethoxy-o-benzoquinone, in a 4:1 ratio, plus 2 mol of methanol for each 1 mol of substrate. Using HRP-catalysed oxidation, we showed that the quinone oxygen atoms are derived from water. We conclude that the three enzymes affect their substrates similarly, and that whether an aromatic compound is a substrate depends in large part on its redox potential. Furthermore, oxidized lignin peroxidase is clearly a stronger oxidant than oxidized HRP or laccase. Determination of the enzyme kinetic parameters for the methoxybenzene oxidations demonstrated further differences among the enzymes.

Benzene Derivatives↗
PubMed1984

Lignin-degrading enzyme from Phanerochaete chrysosporium: Purification, characterization, and catalytic properties of a unique H(2)O(2)-requiring oxygenase.

An extracellular lignin-degrading enzyme from the basidiomycete Phanerochaete chrysosporium Burdsall was purified to homogeneity by ion-exchange chromatography. The 42,000-dalton ligninase contains one protoheme IX per molecule. It catalyzes, nonstereospecifically, several oxidations in the alkyl side chains of lignin-related compounds: C(alpha)-C(beta) cleavage in lignin-related compounds of the type aryl-C(alpha)HOH-C(beta)HR-C(gamma)H(2)OH (R = -aryl or -O-aryl), oxidation of benzyl alcohols to aldehydes or ketones, intradiol cleavage in phenylglycol structures, and hydroxylation of benzylic methylene groups. It also catalyzes oxidative coupling of phenols, perhaps explaining the long-recognized association between phenol oxidation and lignin degradation. All reactions require H(2)O(2). The C(alpha)-C(beta) cleavage and methylene hydroxylation reactions involve substrate oxygenation; the oxygen atom is from O(2) and not H(2)O(2). Thus the enzyme is an oxygenase, unique in its requirement for H(2)O(2).

Journal Article↗
PubMed1986

Peroxidases depolymerize lignin in organic media but not in water.

Horseradish peroxidase and milk lactoperoxidase, while unable to degrade either synthetic or natural lignins in aqueous solutions, vigorously depolymerize polyconiferyl alcohol, milled wood lignin, and kraft pine lignin in dioxane, dimethylformamide, or methyl formate containing 5% aqueous buffer (10 mM acetate, pH 5). Horseradish peroxidase, solubilized in organic media by chemical modification, can also degrade lignin in native lignocellulose (wheat straw).

Journal Article↗
PubMed1990

Glyoxal oxidase of Phanerochaete chrysosporium: its characterization and activation by lignin peroxidase.

Glyoxal oxidase (GLOX) is an extracellular H2O2-generating enzyme produced by ligninolytic cultures of Phanerochaete chrysosporium. The production, purification, and partial characterization of GLOX from agitated cultures are described here. High-oxygen levels are critical for GLOX production as for lignin peroxidase. GLOX purified by anion-exchange chromatography appears homogeneous by NaDod-SO4/PAGE (molecular mass = 68 kDa). However, analysis by isoelectric focusing indicates two major bands (pI 4.7 and 4.9) that stain as glycoproteins as well as for H2O2-producing activity in the presence of methylglyoxal. Purified GLOX shows a marked stimulation in activity when incubated with Cu2+; full activation takes more than 1 hr with 1 mM CuSO4 at pH 6. The steady-state kinetic parameters for the GLOX oxidation of methylglyoxal, glyceraldehyde, dihydroxyacetone, glycolaldehyde, acetaldehyde, glyoxal, glyoxylic acid, and formaldehyde, were determined by using a lignin peroxidase coupled-assay at pH 4.5. Of these substrates, the best is the extracellular metabolite methylglyoxal with a Km of 0.64 mM an apparent rate of catalysis, kcat, of 198 s1 under air-saturated conditions. The Km for oxygen is greater than the concentration of oxygen possible at ambient pressure--i.e., >1.3 mM at 25 degrees C. Importantly, oxygen-uptake experiments show that purified GLOX is inactive unless coupled to the peroxidase reaction. With this coupled reaction, for each mol of methylglyoxal, veratryl alcohol (a lignin peroxidase substrate), and oxygen consumed, 1 mol each of pyruvate and veratraldehyde is produced. The importance of these results is discussed in relation to the physiology of lignin biodegradation and possible extracellular regulatory mechanisms for the control of oxidase and peroxidase activities.

Journal Article↗
PubMed1993

Modelling of the lignin peroxidase LIII of Phlebia radiata: use of a sequence template generated from a 3-D structure.

A model of the lignin peroxidase LIII of Phlebia radiata was constructed on the basis of the structure of cytochrome c peroxidase (CCP). Because of the low percentage of amino acid identity between the CCP and the lignin peroxidase LIII of Phlebia radiata, alignment of the sequences was based on the generation of a template from a knowledge of the 3-D structure of CCP and consensus sequences of lignin peroxidases. This approach gave an alignment in which all the insertions in the lignin peroxidase were placed at loop regions of CCP, with a 21.1% identity for these two proteins. The model was constructed using this alignment and the computer program COMPOSER, which assembles the model as a series of rigid fragments derived from CCP and other proteins. Manual intervention was required for some of the longer loop regions. The alpha-helices forming the structural framework, and especially the haem environment of CCP, are conserved in the LIII model and the core is close packed without holes. A possible site of the substrate oxidation at the haem edge of LIII is discussed.

Amino Acid Sequence↗
PubMed1995

Cellulose-Lignin Interactions (A Computational Study).

Within a broader program of study of the molecular structure of plant cell walls, molecular dynamics calculations were used to explore the character of the motion of lignin model compounds near a cellulose surface. Model cellulose microfibrils, which have a large number of hydroxyl groups on the surface, appear to have a net attractive interaction with the lignin models examined in this study. The lignin monomer coniferyl alcohol rapidly adsorbed onto the surface from a water layer after it was released 13 A from the surface. The major long-range force responsible for this adsorption is likely electrostatic. The attractive interaction is sufficient to restrict the motion of coniferyl alcohol when it is within 1 A of the surface and to orient the phenyl ring parallel to the surface. The [beta]-O-4-linked trimer also was observed to adsorb onto the surface with two of its phenyl rings parallel to the surface. These results suggest a mechanism by which the polysaccharide component of the plant cell wall could influence the structure of lignin. Furthermore, they provide a rationalization of the experimental observation that polysaccharides can change the course of dehydrogenation polymerization of cinnamyl alcohols.

Journal Article↗
PubMed1985

Effects of fungal elicitor on lignin biosynthesis in cell suspension cultures of soybean.

Soybean (Glycine max L.) cells cultured in B5 medium produce extremely low amounts of lignin. However, modification in the growth medium, by lowering the concentration of NO(-) (3) and PO(2-) (4), results in the lignification of these cells without affecting levels of cell wall-esterified 4-coumaric and ferulic acid. The production of an extracellular, macromolecular complex by the cultured soybean cells (Moore TS Jr 1973 Plant Physiol 51: 529-536) allows a rapid, nondestructive solubilization of the lignin which can be estimated by reaction with phloroglucinol in free solution. This system has been used to study the effects of fungal elicitor on the synthesis of lignin in soybean cells. The inclusion of very low levels of an elicitor fraction from the cell walls of Phytophthora megasperma in the medium in which lignification of the soybean cells occurs suppressed both the accumulation of extracellular lignin and phloroglucinol staining of the cell walls without affecting the levels of bound hydroxycinnamic acids. The activity profiles of phenylalanine ammonia-lyase (EC 4.3.1.5) and isoenzymes of 4-coumarate:CoA ligase (EC 6.2.1.12) were compared in lignifying and elicitor-treated cell cultures as was the activity of chalcone synthase, an enzyme of flavonoid biosynthesis. The measured activities of these enzymes in cell cultures treated with elicitor were considerably lower than in untreated cells.

Journal Article↗
PubMed1983

Decolorization of Several Polymeric Dyes by the Lignin-Degrading Basidiomycete Phanerochaete chrysosporium.

The polymeric dyes Poly B-411, Poly R-481, and Poly Y-606 were examined as possible alternatives to the radiolabeled lignin previously used as a substrate in lignin biodegradation assays. Like lignin degradation, the decolorization of these dyes by the white rot basidiomycete Phanerochaete chrysosporium occurred during secondary metabolism, was suppressed in cultures grown in the presence of high levels of nitrogen, and was strongly dependent on the oxygen concentration in the cultures. A variety of inhibitors of lignin degradation, including thiourea, azide, and 4'-O-methylisoeugenol, also inhibited dye decolorization. A pleiotropic mutant of P. chrysosporium, 104-2, lacking phenol oxidase and ligninolytic activity was also not able to decolorize the polymeric dyes, whereas a phenotypic revertant strain, 424-2, regained this capacity. All of these results suggest that the ligninolytic degradation activity of the fungus was responsible for the decolorization of these dyes.

Journal Article↗
PubMed1984

Enhancement of Lignin Degradation in Streptomyces spp. by Protoplast Fusion.

Protoplast fusion was investigated as a technique for genetically manipulating two lignin-degrading Streptomyces strains, Streptomyces viridosporus T7A and Streptomyces setonii 75Vi2. Four of 19 recombinants tested showed enhanced production of acid-precipitable polymeric lignin (APPL), producing 155 to 264% more APPL from corn stover lignocellulose than was produced by the wild-type S. viridosporus T7A. APPLs are lignin degradation intermediates known to be potentially valuable chemical products produced by bioconversion of lignin with Streptomyces spp. The prospects of utilizing protoplast fusion to construct APPL-overproducing Streptomyces strains was considered especially promising.

Journal Article↗
PubMed1984

Screening wood decayed by white rot fungi for preferential lignin degradation.

A screening procedure in which scanning electron microscopy was used indicated that 26 white rot fungi selectively removed lignin from various coniferous and hardwood tree species. Delignified wood from field collections had distinct micromorphological characteristics that were easily differentiated from other types of decay. The middle lamella was degraded, and the cells were separated from one another. Secondary cell wall layers that remained had a fibrillar appearance. Chemical analyses of delignified wood indicated that the cells were composed primarily of cellulose. Only small percentages of lignin and hemicellulose were evident. Delignified wood was not uniformly distributed throughout the decayed wood samples. White-pocket and white-mottled areas of the various decayed wood examined contained delignified cells, but adjacent wood had a nonselective removal of lignin where all cell wall components had been degraded simultaneously. This investigation demonstrates that selective delignification among white rot fungi is more prevalent than previously realized and identifies a large number of fungi for use in studies of preferential lignin degradation.

Journal Article↗
PubMed1985

Anaerobic degradation of soluble fractions of [C-lignin]lignocellulose.

[C-lignin]lignocellulose was solubilized by alkaline heat treatment and separated into different molecular size fractions for use as the sole source of carbon in anaerobic enrichment cultures. This study is aimed at determining the fate of low-molecular-weight, polyaromatic lignin derivatives during anaerobic degradation. Gel permeation chromatography was used to preparatively separate the original C-lignin substrate into three component molecular size fractions, each of which was then fed to separate enrichment cultures. Biodegradability was assessed by monitoring total carbon dioxide and methane production, evolution of labeled gases, loss of C-activity from solution, and changes in gel permeation chromatographic elution patterns. Results indicated that the smaller the size of the molecular weight fraction, the more extensive the degradation to gaseous end products. In addition, up to 30% of the entire soluble lignin-derived carbon was anaerobically mineralized to carbon dioxide and methane.

Journal Article↗
PubMed1987

Initial steps in the pathway for bacterial degradation of two tetrameric lignin model compounds.

We investigated the metabolic route by which a lignin tetramer-degrading mixed bacterial culture degraded two tetrameric lignin model compounds containing beta-O-4 and 5-5 biphenyl structures. The alpha-hydroxyl groups in the propane chain of both phenolic and nonphenolic tetramers were first oxidized symmetrically in two successive steps to give monoketones and diketones. These ketone metabolites were decomposed through C(alpha)(=O)-C(beta) cleavage, forming trimeric carboxyl acids which were further metabolized through another C(alpha)(=O)-C(beta) cleavage. Dehydrodiveratric acid, which resulted from the cleavage of the carbon bonds of the nonphenol tetramer, was demethylated twice. Four metabolites of the phenolic tetramer were purified and identified. All of these were stable compounds in sterile mineral medium, but were readily degraded by lignin tetramer-degrading bacteria along the same pathway as the phenol tetramer. No monoaromatic metabolites accumulated. All metabolites were identified by mass and proton magnetic resonance spectrometry. The metabolic route by which the mixed bacterial culture degraded tetrameric lignin model compounds was different from the route of the main ligninase-catalyzed C(alpha)-C(beta) cleavage by Phanerochaete chrysosporium.

Journal Article↗