Protective effect of dextrans on glucose oxidase denaturation and inactivation

Aspergillus flavipes L-methionine γ-lyase-β-cyclodextrin conjugates with improved stability, catalytic efficiency and anticancer activity

Aspergillus flavipes L-methionine γ-lyase (MGL) has been authenticated as a powerful anticancer agent towards various solid tumors, however, the catalytic efficiency and stability of this enzyme remains the main challenge for its further in vivo applications. Thus, the objective of this study was to enhance the catalytic efficiency, structural stability of A. flavipes MGL, in addition to boost their anticancer activity, via conjugation with β-cyclodextrin. The purified A. flavipes MGL was (38.1 μmol/mg/min) was conjugated with β-cyclodextrin, with immobilization yield 80%. The conjugation process of MGL with β-cyclodextrin was verified from the FTIR analysis, molecular docking analysis, ensuring the covalent conjugation process via the hydrogen, and hydrophobic interactions with the cyclodextrin hydroxyl groups and MGL surface amino acids residues. The free and CD-MGL have the same optimum reaction temperature 37 °C, reaction pH 7.5 and pH stability pH 6.5-8.0. The CD-MGL conjugates had a significant stability to proteinase K and trypsin digestion. The affinity of CD-MGL was increased by ~ 2 folds to L-methionine (KM 3.1 mM), compared to the free one (KM 7.2 mM), as well as the catalytic efficiency of MGL was increased by 1.8 folds upon cyclodextrin conjugation. The higher affinity of CD-MGL for L-methionine might be due to re-orientation of the MGL to bind with the substrate by multiple interactions hydrogen, hydrophobic and covalent bonds compared to the free one. The thermal stability of MGL was increased by ~ 2 folds for the tested treatments, upon cyclodextrin conjugation. The in vitro anticancer activity of CD-MGL was enhanced by 2 folds against the HCT-116 (IC50 value 13.9 μmol/mg/min) and MCF7 (IC50 value 9.6 μmol/mg/min), compared to the free MGL (~ 21.4 μmol/mg/min). The enzymes displayed a significant activity against the proliferation of Ehrlich ascites carcinoma in vivo, with an obvious improvement on the liver tissues, as revealed from the histopathological sections.

A New Exopolysaccharide from a Wood-Decaying Fungus Spongipellis borealis for a Wide Range of Biotechnological Applications

Fungi are a unique natural resource rich in polysaccharides, proteins, and other components. Polysaccharides are considered one of the most important bioactive components in fungi. Increasing numbers of studies have confirmed that fungal polysaccharides have various biological activities. Given these facts, the main aim of this investigation was to carry out isolation, identification, and structural characterisation of a new polysaccharide (EPS) derived from laboratory-cultured vegetative mycelium of a new Spongipellis borealis strain isolated from the environment. The examination of monosaccharides in the EPS demonstrated that the isolated biopolymer was composed mainly of glucose, galactose, and mannose monomers. The analysis of the methylation of the studied polymer indicated that it contained mainly terminal, →3)-linked, →4)-linked, and →2,4)-linked hexoses. The effect of fungal polysaccharides on S. borealis proteolytic enzymes (pepsin, trypsin, and pycnoporopepsin) and laccase activity was determined for the first time. Incubation of the enzyme preparation and EPS showed an influence of EPS on the stability of these enzymes, compared to the control values (without EPS).

Aspergillus Niger thermostable Cytosine deaminase-dextran conjugates with enhanced structure stability, proteolytic resistance, and Antiproliferative activity

Cytosine deaminase (CDA) is a prodrug mediating enzyme converting 5-flurocytosine into 5-flurouracil with profound broad-range anticancer activity towards various cell lines. Availability, molecular stability, and catalytic efficiency are the main limiting factors halting the clinical applications of this enzyme on prodrug and gene therapies, thus, screening for CDA with unique biochemical and catalytic properties was the objective. Thermotolerant/ thermophilic fungi could be a distinctive repertoire for enzymes with affordable stability and catalytic efficiency. Among the recovered thermotolerant isolates, Aspergillus niger with optimal growth at 45 °C had the highest CDA productivity. The enzyme was purified, with purification 15.4 folds, molecular mass 48 kDa and 98 kDa, under denaturing and native PAGE, respectively. The purified CDA was covalently conjugated with dextran with the highest immobilization yield of 75%. The free and CDA-dextran conjugates have the same optimum pH 7.4, reaction temperature 37 °C, and pI 4.5, and similar response to the inhibitors and amino acids suicide analogues, ensuring the lack of effect of dextran conjugation on the CDA conformational structure. CDA-Dextran conjugates had more resistance to proteolysis in response to proteinase K and trypsin by 2.9 and 1.5 folds, respectively. CDA-Dextran conjugates displayed a dramatic structural and thermal stability than the free enzyme, authenticating the acquired structural and catalytic stability upon dextran conjugation. The thermal stability of CDA was increased by about 1.5 folds, upon dextran conjugation, as revealed from the half-life time (T_1/2). The affinity of CDA-conjugates (K_m 0.15 mM) and free CDA (K_m 0.22 mM) to deaminate 5-fluorocytosine was increased by 1.5 folds. Upon dextran conjugation, the antiproliferative activity of the CDA towards the different cell lines "MDA-MB, HepG-2, and PC-3" was significantly increased by mediating the prodrug 5-FC. The CDA-dextran conjugates strongly reduce the tumor size and weight of the Ehrlich cells (EAC), dramatically increase the titers of Caspase-independent apoptotic markers PARP-1 and AIF, with no cellular cytotoxic activity, as revealed from the hematological and biochemical parameters.

Natural microbial polysaccharides as effective factors for modification of the catalytic properties of fungal cellobiose dehydrogenase

Polysaccharides are biopolymers composed of simple sugars like glucose, galactose, mannose, fructose, etc. The major natural sources for the production of polysaccharides include plants and microorganisms. In the present work, four bacterial and two fungal polysaccharides (PS or EPS) were used for the modification and preservation of Pycnoporus sanguineus cellobiose dehydrogenase (CDH) activity. It was found that the presence of polysaccharide preparations clearly enhanced the stability of cellobiose dehydrogenase compared to the control value (4 °C). The highest stabilization effect was observed for CDH modified with Rh110EPS. Changes in the optimum pH in the samples of CDH incubated with the chosen polysaccharide modifiers were evidenced as well. The most significant effect was observed for Rh24EPS and Cu139PS (pH 3.5). Cyclic voltammetry used for the analysis of electrochemical parameters of modified CDH showed the highest peak values after 30 days of incubation with polysaccharides at 4 °C. In summary, natural polysaccharides seem to be an effective biotechnological tool for the modification of CDH activity to increase the possibilities of its practical applications in many fields of industry.

Aspergillus nidulans thermostable arginine deiminase-Dextran conjugates with enhanced molecular stability, proteolytic resistance, pharmacokinetic properties and anticancer activity

The potential anticancer activity of arginine deiminase (ADI) via deimination of l-arginine into citrulline has been extensively verified against various arginine-auxotrophic tumors, however, the higher antigenicity, structural instability and in vivo proteolysis are the major challenges that limit this enzyme from further clinical implementation. Since, this clinically applied enzyme was derived from Mycobacterium spp, thus, searching for ADI from eukaryotic microbes "especially thermophilic fungi" could have a novel biochemical, conformational and catalytic properties. Aspergillus nidulans ADI was purified with 5.3 folds, with molecular subunit structure 48 kDa and entire molecular mass 120 kDa, ensuring its homotrimeric identity. The peptide fingerprinting analysis revealing the domain Glu⁹⁵-Gly⁹⁶-Gly⁹⁷ as the conserved active site of A. nidulans ADI, with higher proximity to Mycobacterium ADI clade IV. In an endeavor to fortify the structural stability and anticancer activity of A. nidulans ADI, the enzyme was chemically modified with dextran. The optimal activity of Dextran-ADI conjugates was determined at 0.08:20 M ratio of ADI: Dextran, with an overall increase to ADI molecular subunit mass to ˜100 kDa. ADI was conjugated with dextran via the ε-amino groups interaction of surface lysine residues of ADI. The resistance of Dextran-ADI conjugate to proteolysis had been increased by 2.5 folds to proteinase K and trypsin, suggesting the shielding of >50% of ADI surface proteolytic recognition sites. The native and Dextran-ADI conjugates have the same optimum reaction temperature (37 °C), reaction pH and pH stability (7.0-8.0) with dependency on K⁺ ions as a cofactor. Dextran-ADI conjugates exhibited a higher thermal stability by ˜ 2 folds for all the tested temperatures, ensuring the acquired structural and catalytic stability upon dextran conjugation. Dextran conjugation slightly protect the reactive amino and thiols groups of surface amino acids of ADI from amino acids suicide inhibitors. The affinity of ADI was increased by 5.3 folds to free L-arginine with a dramatic reduction in citrullination of peptidylarginine residues upon dextran conjugation. The anticancer activity of ADI to breast (MCF-7), liver (HepG-2) and colon (HCT8, HT29, DLD1 and LS174 T) cancer cell lines was increased by 1.7 folds with dextran conjugation in vitro. Pharmacokinetically, the half-life time of ADI was increased by 1.7 folds upon dextran conjugation, in vivo. From the biochemical and hematological parameters, ADIs had no signs of toxicity to the experimental animals. In addition to the dramatic reduction of L-arginine in serum, citrulline level was increased by 2.5 folds upon dextran conjugation of ADI. This is first report exploring thermostable ADI from thermophilic A. nidulans with robust structural stability, catalytic efficiency and proteolytic resistance.

Synthesis of glucose oxidase-PEG aldehyde conjugates and improvement of enzymatic stability

In this article, aldehyde derivative of poly(ethylene glycol) (PEG) was synthesized directly with sodium periodate agent. To obtain a conjugate which possesses better stability, PEG aldehyde was bonded to native enzyme with different molar ratios. The conjugation reaction turned out to be efficient and mild. Colorimetric method was applied to evaluate the enzymatic activity of native GOD and its derivatives by introducing another enzyme, horseradish peroxidase. The GOD-PEG aldehyde conjugate with polymeric chains exhibited reduced enzymatic activity towards the catalytical oxidation of glucose, but with significantly increased thermal stability and elongated lifetime. When GOD was modified with PEG aldehyde the enzymatic activity was decreased 40% at 30 °C. However, when incubated at 60 °C the GOD-PEG aldehyde conjugate still retained the enzyme bioactivity of 40% bioactivity left after 4 h, whereas the native GOD lost almost all the activity in 4 h. The polymer chain attached, the more reduction of the enzymatic activity resulted, however, the longer the lifetime and higher thermal stability of the enzyme obtained.