Structural determination of an exocellular mannan from Rhodotorula mucilaginosa YR-2 using ab initio assignment of proton and carbon NMR spectra

Production, characterization and biological activities of exopolysaccharides from a new cold-adapted yeast: Rhodotorula mucilaginosa sp. GUMS16

Lately, it has been proved that yeast exopolysaccharides (EPS) are potentially applicable biopolymers, a fact that has led to incremental needs for their assessment. The current study is based on the biochemical and molecular level identification of the novel cold-adapted yeast Rhodotorula mucilaginosa sp. GUMS16. Possible antioxidant and antiproliferative activities, as well as extraction and characterization of the GUMS16-produced EPS, were assessed during the course of this study. The results indicated that the strain of GUMS16 is a cold-adapted yeast with growth capability at 4 °C and an approximate EPS production yield of 28.5 g/L which are characterized as highly branched beta-D-glucan having glucose and mannose residues (85:15 mol%, respectively) with an average molecular weight of 84 kDa. In comparison to hyaluronic acid, DPPH, and OH, the scavenging activity attributed to the GUMS16-produced EPS was higher alongside being dose-dependent. The biocompatibility profile of the EPS was well-recognized based on its zero-cytotoxicity rate on a normal cell model. Collectively, the favorable properties of the EPS accentuate their potential as biocompatible compound suitable for subsequent pharmaceutical and industrial applications.

Characterization of Microbial Communities Associated with Ceramic Raw Materials as Potential Contributors for the Improvement of Ceramic Rheological Properties

Technical ceramics are being widely employed in the electric power, medical and engineering industries because of their thermal and mechanical properties, as well as their high resistance qualities. The manufacture of technical ceramic components involves complex processes, including milling and stirring of raw materials in aqueous solutions, spray drying and dry pressing. In general, the spray-dried powders exhibit an important degree of variability in their performance when subjected to dry-pressing, which affects the efficiency of the manufacturing process. Commercial additives, such as deflocculants, biocides, antifoam agents, binders, lubricants and plasticizers are thus applied to ceramic slips. Several bacterial and fungal species naturally occurring in ceramic raw materials, such as Sphingomonas, Aspergillus and Aureobasidium, are known to produce exopolysaccharides. These extracellular polymeric substances (EPS) may confer unique and potentially interesting properties on ceramic slips, including viscosity control, gelation, and flocculation. In this study, the microbial communities present in clay raw materials were identified by both culture methods and DNA-based analyses to select potential EPS producers based on the scientific literature for further assays based on the use of EPS for enhancing the performance of technical ceramics. Potential exopolysaccharide producers were identified in all samples, such as Sphingomonas sp., Pseudomonas xanthomarina, P. stutzeri, P. koreensis, Acinetobacter lwoffi, Bacillus altitudinis and Micrococcus luteus, among bacteria. Five fungi (Penicillium citrinum, Aspergillus niger, Fusarium oxysporum, Acremonium persicinum and Rhodotorula mucilaginosa) were also identified as potential EPS producers.

Stereodivergent Mannosylation Using 2- O-( ortho-Tosylamido)benzyl Group

We report a novel strategy for obtaining both anomers from a single mannosyl donor equipped with a C2- o-TsNHbenzyl ether (2- O-TAB) by switching reaction conditions. In particular, the formation of various β-mannosides was achieved with high selectivity by using a mannosyl phosphite in the presence of ZnI₂.

An inverting β-1,2-mannosidase belonging to glycoside hydrolase family 130 from Dyadobacter fermentans

The glycoside hydrolase family (GH) 130 is composed of inverting phosphorylases that catalyze reversible phosphorolysis of β-D-mannosides. Here we report a glycoside hydrolase as a new member of GH130. Dfer_3176 from Dyadobacter fermentans showed no synthetic activity using α-D-mannose 1-phosphate but it released α-D-mannose from β-1,2-mannooligosaccharides with an inversion of the anomeric configuration, indicating that Dfer_3176 is a β-1,2-mannosidase. Mutational analysis indicated that two glutamic acid residues are critical for the hydrolysis of β-1,2-mannotriose. The two residues are not conserved among GH130 phosphorylases and are predicted to assist the nucleophilic attack of a water molecule in the hydrolysis of the β-D-mannosidic bond.

The alpha-galactomannan Davanat binds galectin-1 at a site different from the conventional galectin carbohydrate binding domain

Galectins are a sub-family of lectins, defined by their highly conserved beta-sandwich structures and ability to bind to beta-galactosides, like Gal beta1-4 Glc (lactose). Here, we used (15)N-(1)H HSQC and pulse field gradient (PFG) NMR spectroscopy to demonstrate that galectin-1 (gal-1) binds to the relatively large galactomannan Davanat, whose backbone is composed of beta1-4-linked d-mannopyranosyl units to which single d-galactopyranosyl residues are periodically attached via alpha1-6 linkage (weight-average MW of 59 kDa). The Davanat binding domain covers a relatively large area on the surface of gal-1 that runs across the dimer interface primarily on that side of the protein opposite to the lactose binding site. Our data show that gal-1 binds Davanat with an apparent equilibrium dissociation constant (K(d)) of 10 x 10(-6) M, compared to 260 x 10(-6) M for lactose, and a stiochiometry of about 3 to 6 gal-1 molecules per Davanat molecule. Mannan also interacts at the same galactomannan binding domain on gal-1, but with at least 10-fold lower avidity, supporting the role of galactose units in Davanat for relatively strong binding to gal-1. We also found that the beta-galactoside binding domain remains accessible in the gal-1/Davanat complex, as lactose can still bind with no apparent loss in affinity. In addition, gal-1 binding to Davanat also modifies the supermolecular structure of the galactomannan and appears to reduce its hydrodynamic radius and disrupt inter-glycan interactions thereby reducing glycan-mediated solution viscosity. Overall, our findings contribute to understanding gal-1-carbohydrate interactions and provide insight into gal-1 function with potentially significant biological consequences.

Sulfated xylomannans isolated from red seaweeds Chondrophycus papillosus and C. flagelliferus (Ceramiales) from Brazil

Sulfated xylomannans were isolated from two species of genus Chondrophycus by aqueous extraction followed by KCl fractionation. Structural determination of the native, desulfated and Smith-degraded KCl-precipitated polysaccharides carried out by composition and methylation analysis and NMR spectroscopy (1D and 2D experiments) showed the following general structure: [see text] These xylomannans present different degrees of branching (15-25%) by beta-D-Xylp (70-80%) and beta-D-Manp-2-S (20-30%) and molecular weights (33-222kDa). This is the first report of the presence of a sulfated xylomannan in species of order Ceramiales.

Direct chemical synthesis of the beta-mannans: linear and block syntheses of the alternating beta-(1-->3)-beta-(1-->4)-mannan common to Rhodotorula glutinis, Rhodotorula mucilaginosa, and Leptospira biflexa

Two stereocontrolled syntheses of a methyl glycoside of an alternating beta-(1-->4)-beta-(1-->3)-mannohexaose, representative of the mannan from Rhodotorula glutinis, Rhodotorula mucilaginosa, and Leptospira biflexa, are described. Both syntheses employ a combination of 4,6-O-benzylidene- and 4,6-O-p-methoxybenzylidene acetal-protected donors to achieve stereocontrolled formation of the beta-mannoside linkage. The first synthesis is a linear one and proceeds with a high degree of stereocontrol throughout and an overall yield of 1.9%. The second synthesis, a block synthesis, makes use of the coupling of two trisaccharides, resulting in a shorter sequence and an overall yield of 4.4%, despite the poor selectivity in the key step.