Engineering of glycoside hydrolase family 7 cellobiohydrolases directed by natural diversity screening

Protein engineering and screening of processive fungal cellobiohydrolases (CBHs) remain challenging due to limited expression hosts, synergy-dependency, and recalcitrant substrates. In particular, glycoside hydrolase family 7 (GH7) CBHs are critically important for the bioeconomy and typically difficult to engineer. Here, we target the discovery of highly active natural GH7 CBHs and engineering of variants with improved activity. Using experimentally assayed activities of genome mined CBHs, we applied sequence and structural alignments to top performers to identify key point mutations linked to improved activity. From ∼1500 known GH7 sequences, an evolutionarily diverse subset of 57 GH7 CBH genes was expressed in Trichoderma reesei and screened using a multiplexed activity screening assay. Ten catalytically enhanced natural variants were identified, produced, purified, and tested for efficacy using industrially relevant conditions and substrates. Three key amino acids in CBHs with performance comparable or superior to Penicillium funiculosum Cel7A were identified and combinatorially engineered into P. funiculosum cel7a, expressed in T. reesei, and assayed on lignocellulosic biomass. The top performer generated using this combined approach of natural diversity genome mining, experimental assays, and computational modeling produced a 41% increase in conversion extent over native P. funiculosum Cel7A, a 55% increase over the current industrial standard T. reesei Cel7A, and 10% improvement over Aspergillus oryzae Cel7C, the best natural GH7 CBH previously identified in our laboratory.

Metabolism of syringyl lignin-derived compounds in Pseudomonas putida enables convergent production of 2-pyrone-4,6-dicarboxylic acid

Valorization of lignin, an abundant component of plant cell walls, is critical to enabling the lignocellulosic bioeconomy. Biological funneling using microbial biocatalysts has emerged as an attractive approach to convert complex mixtures of lignin depolymerization products to value-added compounds. Ideally, biocatalysts would convert aromatic compounds derived from the three canonical types of lignin: syringyl (S), guaiacyl (G), and p-hydroxyphenyl (H). Pseudomonas putida KT2440 (hereafter KT2440) has been developed as a biocatalyst owing in part to its native catabolic capabilities but is not known to catabolize S-type lignin-derived compounds. Here, we demonstrate that syringate, a common S-type lignin-derived compound, is utilized by KT2440 only in the presence of another energy source or when vanAB was overexpressed, as syringate was found to be O-demethylated to gallate by VanAB, a two-component monooxygenase, and further catabolized via extradiol cleavage. Unexpectedly, the specificity (k_cat/K_M) of VanAB for syringate was within 25% that for vanillate and O-demethylation of both substrates was well-coupled to O₂ consumption. However, the native KT2440 gallate-cleaving dioxygenase, GalA, was potently inactivated by 3-O-methylgallate. To engineer a biocatalyst to simultaneously convert S-, G-, and H-type monomers, we therefore employed VanAB from Pseudomonas sp. HR199, which has lower activity for 3MGA, and LigAB, an extradiol dioxygenase able to cleave protocatechuate and 3-O-methylgallate. This strain converted 93% of a mixture of lignin monomers to 2-pyrone-4,6-dicarboxylate, a promising bio-based chemical. Overall, this study elucidates a native pathway in KT2440 for catabolizing S-type lignin-derived compounds and demonstrates the potential of this robust chassis for lignin valorization.

Chimeric cellobiohydrolase I expression, activity, and biochemical properties in three oleaginous yeast

Consolidated bioprocessing using oleaginous yeast is a promising modality for the economic conversion of plant biomass to fuels and chemicals. However, yeast are not known to produce effective biomass degrading enzymes naturally and this trait is essential for efficient consolidated bioprocessing. We expressed a chimeric cellobiohydrolase I gene in three different oleaginous, industrially relevant yeast: Yarrowia lipolytica, Lipomyces starkeyi, and Saccharomyces cerevisiae to study the biochemical and catalytic properties and biomass deconstruction potential of these recombinant enzymes. Our results showed differences in glycosylation, surface charge, thermal and proteolytic stability, and efficacy of biomass digestion. L. starkeyi was shown to be an inferior active cellulase producer compared to both the Y. lipolytica and S. cerevisiae enzymes, whereas the cellulase expressed in S. cerevisiae displayed the lowest activity against dilute-acid-pretreated corn stover. Comparatively, the chimeric cellobiohydrolase I enzyme expressed in Y. lipolytica was found to have a lower extent of glycosylation, better protease stability, and higher activity against dilute-acid-pretreated corn stover.

Is there long-term value of pathology scoring in immunoglobulin A nephropathy? A validation study of the Oxford Classification for IgA Nephropathy (VALIGA) update

Background

It is unknown whether renal pathology lesions in immunoglobulin A nephropathy (IgAN) correlate with renal outcomes over decades of follow-up.

Methods

In 1130 patients of the original Validation Study of the Oxford Classification for IgA Nephropathy (VALIGA) cohort, we studied the relationship between the MEST score (mesangial hypercellularity, M; endocapillary hypercellularity, E; segmental glomerulosclerosis, S; tubular atrophy/interstitial fibrosis, T), crescents (C) and other histological lesions with both a combined renal endpoint [50% estimated glomerular filtration rate (eGFR) loss or kidney failure] and the rate of eGFR decline over a follow-up period extending to 35 years [median 7 years (interquartile range 4.1–10.8)].

Results

In this extended analysis, M1, S1 and T1–T2 lesions as well as the whole MEST score were independently related with the combined endpoint (P < 0.01), and there was no effect modification by age for these associations, suggesting that they may be valid in children and in adults as well. Only T lesions were associated with the rate of eGFR loss in the whole cohort, whereas C showed this association only in patients not treated with immunosuppression. In separate prognostic analyses, the whole set of pathology lesions provided a gain in discrimination power over the clinical variables alone, which was similar at 5 years (+2.0%) and for the whole follow-up (+1.8%). A similar benefit was observed for risk reclassification analyses (+2.7% and +2.4%).

Conclusion

Long-term follow-up analyses of the VALIGA cohort showed that the independent relationship between kidney biopsy findings and the risk of progression towards kidney failure in IgAN remains unchanged across all age groups and decades after the renal biopsy.

Correlation of structure, function and protein dynamics in GH7 cellobiohydrolases from Trichoderma atroviride, T. reesei and T. harzianum

BACKGROUND

The ascomycete fungus Trichoderma reesei is the predominant source of enzymes for industrial conversion of lignocellulose. Its glycoside hydrolase family 7 cellobiohydrolase (GH7 CBH) TreCel7A constitutes nearly half of the enzyme cocktail by weight and is the major workhorse in the cellulose hydrolysis process. The orthologs from Trichoderma atroviride (TatCel7A) and Trichoderma harzianum (ThaCel7A) show high sequence identity with TreCel7A, ~ 80%, and represent naturally evolved combinations of cellulose-binding tunnel-enclosing loop motifs, which have been suggested to influence intrinsic cellobiohydrolase properties, such as endo-initiation, processivity, and off-rate.

RESULTS

The TatCel7A, ThaCel7A, and TreCel7A enzymes were characterized for comparison of function. The catalytic domain of TatCel7A was crystallized, and two structures were determined: without ligand and with thio-cellotriose in the active site. Initial hydrolysis of bacterial cellulose was faster with TatCel7A than either ThaCel7A or TreCel7A. In synergistic saccharification of pretreated corn stover, both TatCel7A and ThaCel7A were more efficient than TreCel7A, although TatCel7A was more sensitive to thermal inactivation. Structural analyses and molecular dynamics (MD) simulations were performed to elucidate important structure/function correlations. Moreover, reverse conservation analysis (RCA) of sequence diversity revealed divergent regions of interest located outside the cellulose-binding tunnel of Trichoderma spp. GH7 CBHs.

CONCLUSIONS

We hypothesize that the combination of loop motifs is the main determinant for the observed differences in Cel7A activity on cellulosic substrates. Fine-tuning of the loop flexibility appears to be an important evolutionary target in Trichoderma spp., a conclusion supported by the RCA data. Our results indicate that, for industrial use, it would be beneficial to combine loop motifs from TatCel7A with the thermostability features of TreCel7A. Furthermore, one region implicated in thermal unfolding is suggested as a primary target for protein engineering.

Percutaneous implant of Denver peritoneo-venous shunt for treatment of refractory ascites: a single center retrospective study

OBJECTIVE

Refractory ascites is defined as a lack of response to high doses of diuretics or the development of diuretic related side effects, which compel the patient to discontinue the diuretic treatment. Current therapeutic strategies include repeated large-volume paracentesis and transjugular intrahepatic portosystemic shunts (TIPS). Peritoneovenous shunt (Denver shunt) should be considered for patients with refractory ascites who are not candidates for paracentesis or TIPS. This study presents our case series in the implant of Denver peritoneovenous shunt.

PATIENTS AND METHODS

Sixty-two patients underwent percutaneous placement of Denver shunt between November 2003 and July 2014. There were 36 men and 26 women. Ascites was secondary to alcoholic cirrhosis in six patients, cryptogenic cirrhosis in six, and virus-related cirrhosis in fifty of them. Liver cirrhosis was classified as Child B in 22 patients and Child C in 40 (no patient was Child A).

RESULTS

All implants were successfully performed. There were no intraoperative problems or lethal complications; our patients were hospitalized for 2 or 3 days. Postoperative complications included: infection of the shunt in 3 patients (4.8%), shunt obstruction in 4 (6.4%) and transient abdominal pain in 4 (6.4%). Significant symptomatic relief was obtained in all patients.

CONCLUSIONS

The percutaneous placement of a Denver shunt is a technically feasible and effective method for symptomatic relief of refractory ascites.

Measurement of volatile organic compounds (VOCs) in libraries and archives in Florence (Italy)

Indoor air samples from libraries and archives in Florence, Italy, were collected and analysed for a variety of volatile organic compounds. The aim was to perform a characterisation of the indoor air quality, and try to elucidate if there are VOCs that may cause or result from the determination of the cultural heritage institutions. All compounds of interest were regularly detected, with BTEXs (Benzene, Toluene, Ethylbenzene, Xylenes) being the most abundant and followed by cyclic volatile methylsiloxanes, aldehydes, terpenes and organic acids. The prevalence and qualitative characteristics, such as concentrations, profiles and indoor/outdoor ratios of BTEXs underline the important influence of the outdoor air infiltrations on the indoor air concentrations. Acetic acid that is a substance that can oxidise books and other exposed objects was detected at concentrations ranging between 1.04 and 18.9μgm^-3, while furfural, that is a known marker of paper degradation, was constantly present at concentrations that ranged between 5.26 and 32.6μgm^-3. This work shows the importance that indoor air quality monitoring campaigns can have in order to give early warning to cultural heritage institution managers about the impact that indoor air quality can have on exposed and/or preserved objects.

Risk Differences Between Prediabetes And Diabetes According To Breast Cancer Molecular Subtypes

Hyperglycemia and hyperinsulinemia may play a role in breast carcinogenesis and prediabetes and diabetes have been associated with increased breast cancer (BC) risk. However, whether BC molecular subtypes may modify these associations is less clear. We therefore investigated these associations in all cases and by BC molecular subtypes among women living in Southern Italy. Cases were 557 patients with non-metastatic incident BC and controls were 592 outpatients enrolled during the same period as cases and in the same hospital for skin-related non-malignant conditions. Adjusted multivariate logistic regression models were built to assess the risks of developing BC in the presence of prediabetes or diabetes. The analyses were repeated by strata of BC molecular subtypes: Luminal A, Luminal B, HER2+, and Triple Negative (TN). Prediabetes and diabetes were significantly associated with higher BC incidence after controlling for known risk factors (OR = 1.94, 95% CI 1.32-2.87 and OR = 2.46, 95% CI 1.38-4.37, respectively). Similar results were seen in Luminal A and B while in the TN subtype only prediabetes was associated with BC (OR = 2.43, 95% CI 1.11-5.32). Among HER2+ patients, only diabetes was significantly associated with BC risk (OR = 3.04, 95% CI 1.24-7.47). Furthermore, when postmenopausal HER2+ was split into hormone receptor positive versus negative, the association with diabetes remained significant only in the former (OR = 5.13, 95% CI 1.53-17.22). These results suggest that prediabetes and diabetes are strongly associated with BC incidence and that these metabolic conditions may be more relevant in the presence of breast cancer molecular subtypes with positive hormone receptors. J. Cell. Physiol. 232: 1144-1150, 2017. © 2016 Wiley Periodicals, Inc.

Body weight and risk of molecular breast cancer subtypes among postmenopausal Mediterranean women

Breast cancer (BC) is the most common malignant tumor in women, obesity is associated with increased BC incidence and mortality and high levels of circulating insulin may negatively impact on cancer incidence. In the present study, we investigated whether the strength of several anthropometric and metabolic parameters varies between BC molecular subtypes. Eligible cases were 991 non-metastatic BC patients recruited between January 2009 and December 2013. Anthropometric, clinical and immunohistochemical features were measured. Multivariate logistic regression models were built to assess HER2 positive BC risk, comparing (a) triple positive (TP) with luminal A, luminal B and triple negative (TN) and (b) HER2-enriched group with luminal A, luminal B and TN. We stratified patients in pre- and post-menopause: significant differences emerged for luminal A in relation to age: they were more likely to be older compared to other groups. Among postmenopausal patients, the adjusted multivariate analysis showed that high BMI and high waist circumference were inversely correlated to TP subtype when compared to luminal B (OR=0.48 and OR=0.49, respectively). Conversely, HOMA-IR was a risk factor for TP when compared to luminal A and TN (OR=2.47 and OR=3.15, respectively). Our findings suggest a potential role of higher abdominal fat in the development of specific BC molecular subtypes in postmenopausal women. Moreover, they support a potential role of insulin resistance in the development of HER2 positive BC, although this role appears to be stronger when hormone receptors are co-expressed, suggesting a difference in the etiology of these two BC subtypes.

Development of Lignocellulosic Biorefinery Technologies: Recent Advances and Current Challenges

Recent developments of the biorefinery concept are described within this review, which focuses on the efforts required to make the lignocellulosic biorefinery a sustainable and economically viable reality. Despite the major research and development endeavours directed towards this goal over the past several decades, the integrated production of biofuel and other bio-based products still needs to be optimized from both technical and economical perspectives. This review will highlight recent progress towards the optimization of the major biorefinery processes, including biomass pretreatment and fractionation, saccharification of sugars, and conversion of sugars and lignin into fuels and chemical precursors. In addition, advances in genetic modification of biomass structure and composition for the purpose of enhancing the efficacy of conversion processes, which is emerging as a powerful tool for tailoring biomass fated for the biorefinery, will be overviewed. The continual improvement of these processes and their integration in the format of a modern biorefinery is paving the way for a sustainable bio-economy which will displace large portions of petroleum-derived fuels and chemicals with renewable substitutes.

Analysis of the role of O-glycosylation in GH51 α-L-arabinofuranosidase from Pleurotus ostreatus

In this study, the recombinant α-L-arabinofuranosidase from the fungus Pleurotus ostreatus (rPoAbf) was subjected to site-directed mutagenesis with the aim of elucidating the role of glycosylation on the properties of the enzyme at the level of S160 residue. As a matter of fact, previous mass spectral analyses had led to the localization of a single O-glycosylation at this site. Recombinant expression and characterization of the rPoAbf mutant S160G was therefore performed. It was shown that the catalytic properties are slightly changed by the mutation, with a more evident modification of the Kcat and KM toward the synthetic substrate pN-glucopyranoside. More importantly, the mutation negatively affected the stability of the enzyme at various pHs and temperatures. Circular dichroism (CD) analyses showed a minimum at 210 nm for wild-type (wt) rPoAbf, typical of the beta-sheets structure, whereas this minimum is shifted for rPoAbf S160G, suggesting the presence of an unfolded structure. A similar behavior was revealed when wt rPoAbf was enzymatically deglycosylated. CD structural analyses of both the site-directed mutant and the enzymatically deglycosylated wild-type enzyme indicate a role of the glycosylation at the S160 residue in rPoAbf secondary structure stability.

Metagenomics for the development of new biocatalysts to advance lignocellulose saccharification for bioeconomic development

The world economy is moving toward the use of renewable and nonedible lignocellulosic biomasses as substitutes for fossil sources in order to decrease the environmental impact of manufacturing processes and overcome the conflict with food production. Enzymatic hydrolysis of the feedstock is a key technology for bio-based chemical production, and the identification of novel, less expensive and more efficient biocatalysts is one of the main challenges. As the genomic era has shown that only a few microorganisms can be cultured under standard laboratory conditions, the extraction and analysis of genetic material directly from environmental samples, termed metagenomics, is a promising way to overcome this bottleneck. Two screening methodologies can be used on metagenomic material: the function-driven approach of expression libraries and sequence-driven analysis based on gene homology. Both techniques have been shown to be useful for the discovery of novel biocatalysts for lignocellulose conversion, and they enabled identification of several (hemi)cellulases and accessory enzymes involved in (hemi)cellulose hydrolysis. This review summarizes the latest progress in metagenomics aimed at discovering new enzymes for lignocellulose saccharification.

Application of a new xylanase activity from Bacillus amyloliquefaciens XR44A in brewer's spent grain saccharification

BACKGROUND

Cellulases and xylanases are the key enzymes involved in the conversion of lignocelluloses into fermentable sugars. Western Ghat region (India) has been recognized as an active hot spot for the isolation of new microorganisms. The aim of this work was to isolate new microorganisms producing cellulases and xylanases to be applied in brewer's spent grain saccharification.

RESULTS

93 microorganisms were isolated from Western Ghat and screened for the production of cellulase and xylanase activities. Fourteen cellulolytic and seven xylanolytic microorganisms were further screened in liquid culture. Particular attention was focused on the new isolate Bacillus amyloliquefaciens XR44A, producing xylanase activity up to 10.5 U mL^-1. A novel endo-1,4-beta xylanase was identified combining zymography and proteomics and recognized as the main enzyme responsible for B. amyloliquefaciens XR44A xylanase activity. The new xylanase activity was partially characterized and its application in saccharification of brewer's spent grain, pretreated by aqueous ammonia soaking, was investigated.

CONCLUSION

The culture supernatant of B. amyloliquefaciens XR44A with xylanase activity allowed a recovery of around 43% xylose during brewer's spent grain saccharification, similar to the value obtained with a commercial xylanase from Trichoderma viride, and a maximum arabinose yield of 92%, around 2-fold higher than that achieved with the commercial xylanase. © 2014 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

The effect of Pleurotus ostreatus arabinofuranosidase and its evolved variant in lignocellulosic biomasses conversion

The fungal arabinofuranosidase from Pleurotus ostreatus PoAbf recombinantly expressed in Pichia pastoris rPoAbf and its evolved variant rPoAbf F435Y/Y446F were tested for their effectiveness to enhance the enzymatic saccharification of three lignocellulosic biomasses, namely Arundo donax, corn cobs and brewer's spent grains (BSG), after chemical or chemical-physical pretreatment. All the raw materials were subjected to an alkaline pretreatment by soaking in aqueous ammonia solution whilst the biomass from A. donax was also pretreated by steam explosion. The capability of the wild-type and mutant rPoAbf to increase the fermentable sugars recovery was assessed by using these enzymes in combination with different (hemi)cellulolytic activities. These enzymatic mixtures were either entirely of commercial origin or contained the cellulase from Streptomyces sp. G12 CelStrep recombinantly expressed in Escherichia coli in substitution to the commercial counterparts. The addition of the arabinofuranosidases from P. ostreatus improved the hydrolytic efficiency of the commercial enzymatic cocktails on all the pretreated biomasses. The best results were obtained using the rPoAbf evolved variant and are represented by increases of the xylose recovery up to 56.4%. These data clearly highlight the important role of the accessory hemicellulolytic activities to optimize the xylan bioconversion yields.

Regulation of cellulase and hemicellulase gene expression in fungi

Research on regulation of cellulases and hemicellulases gene expression may be very useful for increasing the production of these enzymes in their native producers. Mechanisms of gene regulation of cellulase and hemicellulase expression in filamentous fungi have been studied, mainly in Aspergillus and Trichoderma. The production of these extracellular enzymes is an energy-consuming process, so the enzymes are produced only under conditions in which the fungus needs to use plant polymers as an energy and carbon source. Moreover, production of many of these enzymes is coordinately regulated, and induced in the presence of the substrate polymers. In addition to induction by mono- and oligo-saccharides, genes encoding hydrolytic enzymes involved in plant cell wall deconstruction in filamentous fungi can be repressed during growth in the presence of easily metabolizable carbon sources, such as glucose. Carbon catabolite repression is an important mechanism to repress the production of plant cell wall degrading enzymes during growth on preferred carbon sources. This manuscript reviews the recent advancements in elucidation of molecular mechanisms responsible for regulation of expression of cellulase and hemicellulase genes in fungi.

Cloning and recombinant expression of a cellulase from the cellulolytic strain Streptomyces sp. G12 isolated from compost

BACKGROUND

The use of lignocellulosic materials for second generation ethanol production would give several advantages such as minimizing the conflict between land use for food and fuel production, providing less expensive raw materials than conventional agricultural feedstock, allowing lower greenhouse gas emissions than those of first generation ethanol. However, cellulosic biofuels are not produced at a competitive level yet, mainly because of the high production costs of the cellulolytic enzymes. Therefore, this study was aimed at discovering new cellulolytic microorganisms and enzymes.

RESULTS

Different bacteria isolated from raw composting materials obtained from vegetable processing industry wastes were screened for their cellulolytic activity on solid medium containing carboxymethylcellulose. Four strains belonging to the actinomycetes group were selected on the basis of their phenotypic traits and cellulolytic activity on solid medium containing carboxymethylcellulose. The strain showing the highest cellulolytic activity was identified by 16S rRNA sequencing as belonging to Streptomyces genus and it was designated as Streptomyces sp. strain G12. Investigating the enzymes responsible for cellulase activity produced by Streptomyces G12 by proteomic analyses, two endoglucanases were identified. Gene coding for one of these enzymes, named CelStrep, was cloned and sequenced. Molecular analysis showed that the celstrep gene has an open reading frame encoding a protein of 379 amino acid residues, including a signal peptide of 37 amino acid residues. Comparison of deduced aminoacidic sequence to the other cellulases indicated that the enzyme CelStrep can be classified as a family 12 glycoside hydrolase. Heterologous recombinant expression of CelStrep was carried out in Escherichia coli, and the active recombinant enzyme was purified from culture supernatant and characterized. It catalyzes the hydrolysis of carboxymethylcellulose following a Michaelis-Menten kinetics with a KM of 9.13 mg/ml and a vmax of 3469 μM min-1. The enzyme exhibits a half life of around 24 h and 96 h at 60°C and 50°C, respectively and shows a retention of around 80% of activity after 96 h at 40°C.

CONCLUSIONS

In this manuscript, we describe the isolation of a new cellulolytic strain, Streptomyces sp. G12, from industrial waste based compost, the identification of the enzymes putatively responsible for its cellulolytic activity, the cloning and the recombinant expression of the gene coding for the Streptomyces sp. G12 cellulase CelStrep, that was characterized showing to exhibit a relevant thermoresistance increasing its potential for cellulose conversion.

Industrial waste based compost as a source of novel cellulolytic strains and enzymes

Ninety bacteria isolated from raw composting materials were screened for their cellulolytic activity on solid medium containing carboxymethylcellulose. The bacteria producing the highest cellulolytic activity levels were identified by 16S rRNA sequencing as Bacillus licheniformis strain 1, Bacillus subtilis subsp. subtilis strain B7B, Bacillus subtilis subsp. spizizenii strain 6, and Bacillus amyloliquefaciens strain B31C. Cellulase activity production by the most productive strain B. amyloliquefaciens B31C was optimized in liquid culture varying the carbon source. Comparison of growth curves of B. amyloliquefaciens B31C at temperatures from 28 to 47 °C indicated its thermotolerant nature. Moreover, analysis of time courses of cellulase activity production in this thermal range showed that increase of temperature from 28 to 37 °C causes an increase of cellulase activity levels. Investigating the enzymes responsible for cellulase activity produced by B. amyloliquefaciens B31C by proteomic analyses, an endoglucanase was identified. It was shown that the purified enzyme catalyzes carboxymethylcellulose's hydrolysis following Michaelis-Menten kinetics with a K(M) of 9.95 mg ml(-1) and a v(max) of 284 μM min(-1) . It shows a retention of 90% of its activity for at least 144 h of incubation at 40 °C and exhibits a range of optimum temperatures from 50 to 70 °C.

Characterization of laccase isoforms produced by Pleurotus ostreatus in solid state fermentation of sugarcane bagasse

Laccases are oxidative enzymes linked to biological degradation of lignin. The aim of this work was to evaluate the effect of inducers and different concentrations of nitrogen on production level of total laccase activity and pattern of laccase isoforms, produced in solid state fermentation of sugarcane bagasse by a selected strain of Pleurotus ostreatus. The addition of yeast extract 5 g/L, copper sulfate 150 μM and ferulic acid 2 mM provided highest enzymatic activity (167 U/g) and zymograms indicated the presence of six laccase isoforms (POXA1b, POXA3, POXC and three other isoforms). Results of protein identification by mass spectrometry confirmed the presence of POXC and POXA3 as the main isoenzymes, and also identified a glyoxal oxidase and three galactose oxidases. The fact that the isoenzyme POXA1b was not identified in the analyzed samples can be possibly explained by its sensitivity to protease degradation.

A family GH51 α-L-arabinofuranosidase from Pleurotus ostreatus: identification, recombinant expression and characterization

An α-L-arabinofuranosidase produced by Pleurotus ostreatus (PoAbf) during solid state fermentation on tomato pomace was identified and the corresponding gene and cDNA were cloned and sequenced. Molecular analysis showed that the poabf gene carries 26 exons interrupted by 25 introns and has an open reading frame encoding a protein of 646 amino acid residues, including a signal peptide of 20 amino acid residues. The amino acid sequence similar to the other α-L-arabinofuranosidases indicated that the enzyme encoded by poabf can be classified as a family 51 glycoside hydrolase. Heterologous recombinant expression of PoAbf was carried out in the yeasts Pichia pastoris and Kluyveromyces lactis achieving the highest production level of the secreted enzyme (180 mg L(-1)) in the former host. rPoAbf produced in P. pastoris was purified and characterized. It is a glycosylated monomer with a molecular weight of 81,500 Da in denaturing conditions. Mass spectral analyses led to the localization of a single O-glycosylation site at the level of Ser160. The enzyme is highly specific for α-L-arabinofuranosyl linkages and when assayed with p-nitrophenyl α-L-arabinofuranoside it follows Michaelis-Menten kinetics with a K (M) of 0.64 mM and a k (cat) of 3,010 min(-1). The optimum pH is 5 and the optimal temperature 40°C. It is worth noting that the enzyme shows a very high stability in a broad range of pH. The more durable activity showed by rPoAbf in comparison to the other α-L-arabinofuranosidases enhances its potential for biotechnological applications and increases interest in elucidating the molecular bases of its peculiar properties.

Fungal solid state fermentation on agro-industrial wastes for acid wastewater decolorization in a continuous flow packed-bed bioreactor

This study was aimed at developing a process of solid state fermentation (SSF) with the fungi Pleurotus ostreatus and Trametes versicolor on apple processing residues for wastewater decolorization. Both fungi were able to colonize apple residues without any addition of nutrients, material support or water. P. ostreatus produced the highest levels of laccases (up to 9U g(-1) of dry matter) and xylanases (up to 80U g(-1) of dry matter). A repeated batch decolorization experiment was set up with apple residues colonized by P. ostreatus, achieving 50% decolorization and 100% detoxification after 24h, and, adding fresh wastewater every 24h, a constant decolorization of 50% was measured for at least 1 month. A continuous decolorization experiment was set up by a packed-bed reactor based on colonized apple residues achieving a performance of 100mg dye L(-1)day(-1) at a retention time of 50h.

Oxidative stress in IgA nephropathy

IgA nephropathy (IgAN) is characterized by mesangial deposits of IgA1, likely due to accumulation of IgA immune complexes. The activation of intracellular signaling mostly results in oxidative stress, as detected in mesangial cells cultured with aberrantly glycosylated IgA or IgA aggregates and in renal biopsies of patients with IgAN. Signs of altered oxidation/antioxidation balance have been detected in sera and/or in erythrocytes of patients with IgAN, including increased levels of lipoperoxide or malondialdehyde and reduced activity of superoxide dismutase, catalase and glutathione peroxidase. Moreover, increased levels of a marker of oxidative stress, advanced oxidation protein products (AOPPs), have been reported to be significantly associated with proteinuria and disease progression in patients with IgAN. AOPPs are often carried by albumin and can in turn enhance the oxidative stress in the circulation. Recent research suggests that the nephrotoxicity of aberrantly glycosylated IgA1 in IgAN is enhanced in the presence of systemic signs of oxidative stress, and it is tempting to hypothesize that the level of the oxidative milieu conditions the different expression and progression of IgAN.