Fast and efficient purification of chloroperoxidase from C. fumago

Identification and Expression of New Unspecific Peroxygenases - Recent Advances, Challenges and Opportunities

In 2004, the fungal heme-thiolate enzyme subfamily of unspecific peroxygenases (UPOs) was first described in the basidiomycete Agrocybe aegerita. As UPOs naturally catalyze a broad range of oxidative transformations by using hydrogen peroxide as electron acceptor and thus possess a great application potential, they have been extensively studied in recent years. However, despite their versatility to catalyze challenging selective oxyfunctionalizations, the availability of UPOs for potential biotechnological applications is restricted. Particularly limiting are the identification of novel natural biocatalysts, their production, and the description of their properties. It is hence of great interest to further characterize the enzyme subfamily as well as to identify promising new candidates. Therefore, this review provides an overview of the state of the art in identification, expression, and screening approaches of fungal UPOs, challenges associated with current protein production and screening strategies, as well as potential solutions and opportunities.

Liquid-liquid extraction of antimicrobial peptide P34 by aqueous two-phase and micellar systems

Antimicrobial peptide P34 is a promising biopreservative for utilization in the food industry. In this work, aqueous biphasic systems (ABS) and aqueous biphasic micellar systems (ABMS) were studied as prestep for purification of peptide P34. The ABS was prepared with polyethylene glycol (PEG) and inorganic salts and the ABMS with Triton X-114 was chosen as the phase-forming surfactant. Results indicate that peptide P34 partitions preferentially to PEG-rich phase and extraction with ammonium sulfate [(NH₄)₂SO₄], yielding a 75% recovery of the antimicrobial activity, specific activity of 1,530 antimicrobial units per mg of protein, and purification fold of 2.48. Protein partition coefficient and partition coefficient for the biological activity with (NH₄)₂SO₄ system were 0.48 and 64, respectively. Addition of sodium chloride did not affect recovery, but decreased protein amount in the PEG-rich phase, indicating a higher partition of biomolecules. ABMS did not yield good recovery of antimicrobial activity. Purification fold using PEG-(NH₄)₂SO₄ and 1.0 mol l^-1 sodium chloride was twice higher than that obtained by conventional protocol, indicating a successful utilization of ABS as a step for purification of peptide P34.

The taming of oxygen: biocatalytic oxyfunctionalisations

The scope and limitations of oxygenases as catalysts for preparative organic synthesis is discussed.

Silica Sol-Gel Entrapment of the Enzyme Chloroperoxidase

The enzyme chloroperoxidase (CPO) was immobilized in silica sol-gel beads prepared from tetramethoxysilane. The average pore diameter of the silica host structure (~3 nm) was smaller than the globular CPO diameter (~6 nm) and the enzyme remained entrapped after sol-gel maturation. The catalytic performance of the entrapped enzyme was assessed via the pyrogallol peroxidation reaction. Sol-gel beads loaded with 4 μg CPO per mL sol solution reached 9–12% relative activity compared to free CPO in solution. Enzyme kinetic analysis revealed a decrease inkcatbut no changes inKMorKI. Product release or enzyme damage might thus limit catalytic performance. Yet circular dichroism and visible absorption spectra of transparent CPO sol-gel sheets did not indicate enzyme damage. Activity decline due to methanol exposure was shown to be reversible in solution. To improve catalytic performance the sol-gel protocol was modified. The incorporation of 5, 20, or 40% methyltrimethoxysilane resulted in more brittle sol-gel beads but the catalytic performance increased to 14% relative to free CPO in solution. The use of more acidic casting buffers (pH 4.5 or 5.5 instead of 6.5) resulted in a more porous silica host reaching up to 18% relative activity.

Identification of a Caldariomyces fumago mutant secreting an inactive form of chloroperoxidase lacking the heme group and N-glycans

By mutant colony screening of Caldariomyces fumago a mutant was isolated which was slightly greenish on fructose minimal medium and grew slower in comparison to the wild type. The supernatant samples lacked the Soret band typical for the heme group of the CPO and nearly no CPO activity was detected. SDS-PAGE analysis of mutant culture supernatant samples showed production of a 38–40 kDa protein while wild type samples contain the 42 kDa CPO protein. Protein identification using nanoLC-ESI-MS/MS was performed and based on three peptides the protein in the mutant culture was identified as CPO. No differences in the CPO gene sequences of wild type and mutant were found indicating a post-translational defect in protein maturation. Deglycosylation experiments using CPO from wild type and mutant were carried out. After removing N-linked oligosaccharides from wild type CPO a protein band at 38–40 kDa was detected. Our results reveal that the mutant protein lacks the heme group as well as the N-glycans.

White mutants of chloroperoxidase-secreting Caldariomyces fumago as superior production strains, revealing an interaction between pigmentation and enzyme secretion

By mutant-colony screening of Caldariomyces fumago, several white mutants were isolated that are superior strains for the production of the valuable enzyme chloroperoxidase (CPO). Their culture supernatant lacks the contaminating dark pigment, which simplifies downstream processing. Furthermore, the CPO content increased significantly faster than the wild-type rate, which uncovers possible interactions between pigmentation and enzyme secretion.

A thermostable humic acid peroxidase from Streptomyces sp. strain AH4: purification and biochemical characterization

An extracellular thermostable humic acid peroxidase (HaP3) was isolated from a Streptomyces sp. strain AH4. MALDI-TOF MS analysis showed that the purified enzyme was a monomer with a molecular mass of 60,215.18Da. The 26N-terminal residues of HaP3 displayed high homology with Streptomyces peroxidases. Optimal peroxidase activity was obtained at pH 5 and 80°C. HaP3 was stable at pH and temperature ranges of 4-8 and 60-90°C for 72 and 4h, respectively. HaP3 catalyzed the oxidation of 2,4-dichlorophenol, commercial humic acid, guiacol, and 2,6-dichlorophenol (50mM); L-3,4-dihydroxyphenylalanine (40 mM); 4-chlorophenol, 2,4,5-trichlorophenol, and 2,4,6-trichlorophenol (30 mM) in the presence of hydrogen peroxide. Sodium azide and potassium cyanide inhibited HaP3, which indicated the presence of heme components. These properties make HaP3 a potential strong candidate for future application in the elimination of natural humic acids in drinking water.

Biocatalysed halogenation of nucleobase analogues

The synthesis of halogenated nucleosides and nucleobases is of interest due to their chemical and pharmacological applications. Herein, the enzymatic halogenation of nucleobases and analogues catalysed by microorganisms and by chloroperoxidase from Caldariomyces fumago has been studied. This latter enzyme catalysed the chlorination and bromination of indoline and uracil. Pseudomonas, Citrobacter, Aeromonas, Streptomyces, Xanthomonas, and Bacillus genera catalysed the chlorination and/or bromination of indole and indoline. Different products were obtained depending on the substrate, the biocatalyst and the halide used. In particular, 85% conversion from indole to 5-bromoindole was achieved using Streptomyces cetonii.