Non-Specific GH30_7 Endo-β-1,4-xylanase from Talaromyces leycettanus

This study describes the catalytic properties of a GH30_7 xylanase produced by the fungus Talaromyces leycettanus. The enzyme is an ando-β-1,4-xylanase, showing similar specific activity towards glucuronoxylan, arabinoxylan, and rhodymenan (linear β-1,3-β-1,4-xylan). The heteroxylans are hydrolyzed to a mixture of linear as well as branched β-1,4-xylooligosaccharides that are shorter than the products generated by GH10 and GH11 xylanases. In the rhodymenan hydrolyzate, the linear β-1,4-xylooligosaccharides are accompanied with a series of mixed linkage homologues. Initial hydrolysis of glucuronoxylan resembles the action of other GH30_7 and GH30_8 glucuronoxylanases, resulting in a series of aldouronic acids of a general formula MeGlcA2Xyln. Due to the significant non-specific endoxylanase activity of the enzyme, these acidic products are further attacked in the unbranched regions, finally yielding MeGlcA2Xyl2-3. The accommodation of a substituted xylosyl residue in the −2 subsite also applies in arabinoxylan depolymerization. Moreover, the xylose residue may be arabinosylated at both positions 2 and 3, without negatively affecting the main chain cleavage. The catalytic properties of the enzyme, particularly the great tolerance of the side-chain substituents, make the enzyme attractive for biotechnological applications. The enzyme is also another example of extraordinarily great catalytic diversity among eukaryotic GH30_7 xylanases.

Biodegradable and Transparent Films With Tunable UV-blocking Property From Xylose Residue by a Top-down Approach

As over exposure of the earth to ultraviolet (UV) light and increased amount of petroleum-based plastic waste, biodegradable UV-blocking materials are desired for diverse sustainable applications. Xylose residue, as the byproduct of xylitol production from corn cobs, is mainly composed of cellulose and lignin. Here, we develop a series of xylose residue films through a top-down approach (i.e., tunable delignification and regeneration) without any additional additives. The treated xylose residues with lignin content of 4.4-29.7% are used to prepare regenerated films, which exhibit excellent UV-blocking capability: 68.6-99.2% for UVB (290-320 nm) and 47.1-98.2% for UVA (320-400 nm). Moreover, these films remain a great optical transparency (50.6-86.6%) and show enhanced water vapor permeability (2.17-2.76 ×10-11 g·cm·cm-2·s-1·mmHg-1), surface hydrophobicity (water contact angle=72.3-86.4°), and thermal stability. Overall, our sustainable UV-blocking films have potential applications in the fields of electronics, food packaging, and windshields, etc. This study provides new insights into converting xylose residue directly to high value-added functional bioproducts.

Structural Characterization and Antioxidant Activity of Milled Wood Lignin from Xylose Residue and Corncob

Xylose residue (XR), after diluted acid treatment of corncob, consists of cellulose and lignin. However, structural changes of XR lignin have not been investigated comprehensively, and this has seriously hindered the efficient utilization of lignin. In this study, corncob milled wood lignin (CC MWL), and xylose residue milled wood lignin (XR MWL) were isolated according to the modified milled wood lignin (MWL) method. The structural features of two lignin fractions were thoroughly investigated via fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), thermogravimetric analysis (TGA) and two dimensional nuclear magnetic resonance (2D NMR) spectroscopy techniques. XR MWL with higher yield and lower bound carbohydrate contents presented more phenolic OH contents than CC MWL due to partial cleavage of β-O-4. Furthermore, the molecular weights of XR MWL were increased, possibly because of condensation of the lignin during the xylose production. A study on antioxidant activity showed that XR lignin had better radical scavenging ability than that of 2,6-Di-tert-butyl-4-methyl-phenol (BHT) and CC MWL. The results suggested that the lignin in xylose residue, showing great antioxidant properties, has potential applications in food additives.

FAM20B is a kinase that phosphorylates xylose in the glycosaminoglycan–protein linkage region

2-O-phosphorylation of xylose has been detected in the glycosaminoglycan–protein linkage region, GlcAβ1-3Galβ1-3Galβ1-4Xylβ1-O-Ser, of proteoglycans. Recent mutant analyses in zebrafish suggest that xylosyltransferase I and FAM20B, a protein of unknown function that shows weak similarity to a Golgi kinase encoded by four-jointed, operate in a linear pathway for proteoglycan production. In the present study, we identified FAM20B as a kinase that phosphorylates the xylose residue in the linkage region. Overexpression of FAM20B increased the amount of both chondroitin sulfate and heparan sulfate in HeLa cells, whereas the RNA interference of FAM20B resulted in a reduction of their amount in the cells. Gel-filtration analysis of the glycosaminoglycan chains synthesized in the overexpressing cells revealed that the glycosaminoglycan chains had a similar length to those in mock-transfected cells. These results suggest that FAM20B regulates the number of glycosaminoglycan chains by phosphorylating the xylose residue in the glycosaminoglycan–protein linkage region of proteoglycans.

Functional Characterization of a Novel Xylanase from a Corn Strain of Erwinia chrysanthemi

ABSTRACT A β-1,4-xylan hydrolase (xylanase A) produced by Erwinia chrysanthemi D1 isolated from corn was analyzed with respect to its secondary structure and enzymatic function. The pH and temperature optima for the enzyme were found to be pH 6.0 and 35°C, with a secondary structure under those conditions that consists of approximately 10 to 15% α-helices. The enzyme was still active at temperatures higher than 40°C and at pHs of up to 9.0. The loss of enzymatic activity at temperatures above 45°C was accompanied by significant loss of secondary structure. The enzyme was most active on xylan substrates with low ratios of xylose to 4-O-methyl-d-glucuronic acid and appears to require two 4-O-methyl-d-glucuronic acid residues for substrate recognition and/or cleavage of a β-1,4-xylosidic bond. The enzyme hydrolyzed sweetgum xylan, generating products with a 4-O-methyl-glucuronic acid-substituted xylose residue one position from the nonreducing terminus of the oligoxyloside product. No internal cleavages of the xylan backbone between substituted xylose residues were observed, giving the enzyme a unique mode of action in the hydrolysis compared to all other xylanases that have been described. Given the size of the oligoxyloside products generated by the enzyme during depolymerization of xylan substrates, the function of the enzyme may be to render substrate available for other depolymerizing enzymes instead of producing oligoxylosides for cellular metabolism and may serve to produce elicitors during the initiation of the infectious process.

Phenotypic Switching in Cryptococcus neoformansResults in Changes in Cellular Morphology and Glucuronoxylomannan Structure

ABSTRACT Cryptococcus neoformans strains exhibit variability in their capsular polysaccharide, cell morphology, karyotype, and virulence, but the relationship between these variables is poorly understood. A hypovirulent C. neoformans 24067A isolate, which usually produces smooth (SM) colony types, was found to undergo phenotypic switching and to produce wrinkled (WR) and pseudohyphal (PH) colony types at frequencies of approximately 10−4 to 10−5 when plated on Sabouraud agar. Cells from these colony types had large polysaccharide capsules and PH morphology, respectively. Scanning electron microscopy showed that different colony types were the result of altered cellular packing in the colony. Phenotypic switching was associated with quantitative and qualitative changes in capsular polysaccharide. Specifically, the glucuronoxylomannan (GXM) of the WR polysaccharide differed in the proportion of structural reporter groups and in increased xylose residue content linked at the 4 to 0 position. The relative virulence of the colony types was WR > PH > SM, as measured by CFU in rat lungs after intratracheal infection. Karyotype instability was observed in strain 24067A and involved primarily two chromosomes. Colonies with an alternative colony type exhibited more karyotype changes, which did not revert to the original karyotype in reverted colonies. In summary, this study revealed that phenotypic switching inC. neoformans (i) can produce WR colonies consisting of cells with either large capsule or PH morphology, (ii) is associated with production of structurally different GXM, (iii) is commonly associated with karyotype changes, (iv) can produce cells of PH morphology, and (v) can increase the virulence of a strain. Hence, phenotypic switching is an adaptive mechanism linked to virulence that can generate cell types with very different biological characteristics.