Recombinant expression of an l-amino acid oxidase from the fungus Hebeloma cylindrosporum in Pichia pastoris including fermentation

Crystal structure and enzyme engineering of the broad substrate spectrum l-amino acid oxidase 4 from the fungus Hebeloma cylindrosporum

l-Amino acid oxidases (LAAOs) catalyze the oxidative deamination of l-amino acids to α-keto acids. Recombinant production of LAAOs with broad substrate spectrum remains a formidable challenge. We previously achieved this for the highly active and thermostable LAAO4 of Hebeloma cylindrosporum (HcLAAO4). Here, we crystallized a proteolytically truncated surface entropy reduction variant of HcLAAO4 and solved its structure in substrate-free form and in complex with diverse substrates. The ability to support the aliphatic portion of a substrate's side chain by an overall hydrophobic active site is responsible for the broad substrate spectrum of HcLAAO4, including l-amino acids with big aromatic, acidic and basic side chains. Based on the structural findings, we generated an E288H variant with increased activity toward pharmaceutical building blocks of high interest.

Improvement of Heterologous Soluble Expression of L-amino Acid Oxidase Using Logistic Regression

Successful implementation of enzymes in practical application hinges on the development of efficient mass production techniques. However, in a heterologous expression system, the protein is often unable to fold correctly and, thus, forms inclusion bodies, resulting in the loss of its original activity. In this study, we present a new and more accurate model for predicting amino acids associated with an increased L-amino acid oxidase (LAO) solubility. Expressing LAO from Rhizoctonia solani in Escherichia coli and combining random mutagenesis and statistical logistic regression, we modified 108 amino acid residues by substituting hydrophobic amino acids with serine and hydrophilic amino acids with alanine. Our results indicated that specific mutations in Euclidean distance, glycine, methionine, and secondary structure increased LAO expression. Furthermore, repeated mutations were performed for LAO based on logistic regression models. The mutated LAO displayed a significantly increased solubility, with the 6-point and 58-point mutants showing a 2.64- and 4.22-fold increase, respectively, compared with WT-LAO. Ultimately, using recombinant LAO in the biotransformation of α-keto acids indicates its great potential as a biocatalyst in industrial production.

Co-Immobilization of a Multi-Enzyme Cascade: (S)-Selective Amine Transaminases, l-Amino Acid Oxidase and Catalase

An enzyme cascade was established previously consisting of a recycling system with an l-amino acid oxidase (hcLAAO4) and a catalase (hCAT) for different α-keto acid co-substrates of (S)-selective amine transaminases (ATAs) in kinetic resolutions of racemic amines. Only 1 mol % of the co-substrate was required and l-amino acids instead of α-keto acids could be applied. However, soluble enzymes cannot be reused easily. Immobilization of hcLAAO4, hCAT and the (S)-selective ATA from Vibrio fluvialis (ATA-Vfl) was addressed here. Immobilization of the enzymes together rather than on separate beads showed higher reaction rates most likely due to fast co-substrate channeling between ATA-Vfl and hcLAAO4 due to their close proximity. Co-immobilization allowed further reduction of the co-substrate amount to 0.1 mol % most likely due to a more efficient H2 O2 -removal caused by the stabilized hCAT and its proximity to hcLAAO4. Finally, the co-immobilized enzyme cascade was reused in 3 cycles of preparative kinetic resolutions to produce (R)-1-PEA with high enantiomeric purity (97.3 %ee). Further recycling was inefficient due to the instability of ATA-Vfl, while hcLAAO4 and hCAT revealed high stability. An engineered ATA-Vfl-8M was used in the co-immobilized enzyme cascade to produce (R)-1-(3-ethoxy-4-methoxyphenyl)-2-(methylsulfonyl)ethanamine, an apremilast-intermediate, with a 1,000 fold lower input of the co-substrate.

Recombinant L-Amino Acid Oxidase with broad substrate spectrum for Co-Substrate Recycling in (S)-Selective Transaminase-Catalyzed Kinetic Resolutions

Chiral and enantiopure amines can be produced by enantioselective transaminases via kinetic resolution of amine racemates. This transamination reaction requires stoichiometric amounts of co-substrate. A dual-enzyme recycling system overcomes this limitation: L-amino acid oxidases (LAAO) recycle the accumulating co-product of ( S )-selective transaminases in the kinetic resolution of racemic amines to produce pure ( R )-amines. However, availability of suitable LAAOs is limited. Here we use the heterologously produced, highly active fungal hcLAAO4 with broad substrate spectrum. H 2 O 2 as by-product of hcLAAO4 is detoxified by a catalase. The final system allows using sub-stoichiometric amounts of 1 mol% of the transaminase co-substrate as well as the initial application of L-amino acids instead of α-keto acids. With an optimized protocol, synthetic potential of this kinetic resolution cascade was proven at the preparative scale (>90 mg) by the synthesis of highly enantiomerically pure ( R )-methylbenzylamine (>99 %ee) at complete conversion (50 %).

Analysis of N-glycosylation in fungal l-amino acid oxidases expressed in the methylotrophic yeast Pichia pastoris

l-amino acid oxidases (LAAOs) catalyze the oxidative deamination of l-amino acids to corresponding α-keto acids. Here, we describe the heterologous expression of four fungal LAAOs in Pichia pastoris. cgLAAO1 from Colletotrichum gloeosporioides and ncLAAO1 from Neurospora crassa were able to convert substrates not recognized by recombinant 9His-hcLAAO4 from the fungus Hebeloma cylindrosporum described earlier thereby broadening the substrate spectrum for potential applications. 9His-frLAAO1 from Fibroporia radiculosa and 9His-laLAAO2 from Laccaria amethystine were obtained only in low amounts. All four enzymes were N-glycosylated. We generated mutants of 9His-hcLAAO4 lacking N-glycosylation sites to further understand the effects of N-glycosylation. All four predicted N-glycosylation sites were glycosylated in 9His-hcLAAO4 expressed in P. pastoris. Enzymatic activity was similar for fully glycosylated 9His-hcLAAO4 and variants without one or all N-glycosylation sites after acid activation of all samples. However, activity without acid treatment was low in a variant without N-glycans. This was caused by the absence of a hypermannosylated N-glycan on asparagine residue N54. The lack of one or all of the other N-glycans was without effect. Our results demonstrate that adoption of a more active conformation requires a specific N-glycosylation during biosynthesis.

Antimicrobial properties of L-amino acid oxidase: biochemical features and biomedical applications

Abstract

Mucus layer that covers the body surface of various animal functions as a defense barrier against microbes, environmental xenobiotics, and predators. Previous studies have reported that L-amino acid oxidase (LAAO), present in several animal fluids, has potent properties against pathogenic bacteria, viruses, and parasites. LAAO catalyzes the oxidative deamination of specific L-amino acids with the generation of hydrogen peroxide and L-amino acid metabolites. Further, the generated hydrogen peroxide is involved in oxidation (direct effect) while the metabolites activate immune responses (indirect effect). Therefore, LAAO exhibits two different mechanisms of bioactivation. Previously, we described the selective, specific, and local oxidative and potent antibacterial actions of various LAAOs as potential therapeutic strategies. In this review, we focus on their biochemical features, enzymatic regulations, and biomedical applications with a view of describing their probable role as biochemical agents and biomarkers for microbial infections, cancer, and autoimmune-mediated diseases. We consider that LAAOs hold implications in biomedicine owing to their antimicrobial activity wherein they can be used in treatment of infectious diseases and as diagnostic biomarkers in the above-mentioned diseased conditions.

Key points

•Focus on biochemical features, enzymatic regulation, and biomedical applications of LAAOs.

•Mechanisms of antimicrobial activity, inflammatory regulation, and immune responses of LAAOs.

•Potential biomedical application as an antimicrobial and anti-infection agent, and disease biomarker.

Recombinant expression of an l-amino acid oxidase from the fungus Hebeloma cylindrosporum in Pichia pastoris including fermentation

l‐amino acid oxidases (LAAOs) are flavoenzymes that catalyze the oxidative deamination of l‐amino acids to the corresponding α‐keto acids, ammonia, and hydrogen peroxide. Here, we show the overexpression, purification, and the characterization of LAAO4 from the fungus Hebeloma cylindrosporum in the yeast Pichia pastoris with a 9His‐tag and compare this with the recently characterized 6His‐hcLAAO4 expressed in E. coli. The expression of the enzyme with an ER‐signal sequence in P. pastoris resulted in a glycosylated, secreted protein. The enzymatic activity without activation was higher after expression in P. pastoris compared to E. coli. Due to treatment with acidic pH, a striking increase of activity could be detected for both expression systems resulting in similar specific activities after acid activation. Regarding the substrate spectrum, temperature stability, K_m, and v_max values, hcLAAO4 showed very few differences when produced in these two expression systems. A higher yield of hcLAAO4 could be obtained by fermentation.