Cloning, expression and biochemical characterization of xanthine and adenine phosphoribosyltransferases from Thermus thermophilus HB8

A Multi-enzyme Cascade for the Biosynthesis of AICA Ribonucleoside Di- and Triphosphate

AICA (5'-aminoimidazole-4-carboxamide) ribonucleotides with different phosphorylation levels are the pharmaceutically active metabolites of AICA nucleoside-based drugs. The chemical synthesis of AICA ribonucleotides with defined phosphorylation is challenging and expensive. In this study, we describe two enzymatic cascades to synthesize AICA derivatives with defined phosphorylation levels from the corresponding nucleobase and the co-substrate phosphoribosyl pyrophosphate. The cascades are composed of an adenine phosphoribosyltransferase from Escherichia coli (EcAPT) and different polyphosphate kinases: polyphosphate kinase from Acinetobacter johnsonii (AjPPK), and polyphosphate kinase from Meiothermus ruber (MrPPK). The role of the EcAPT is to bind the nucleobase to the sugar moiety, while the kinases are responsible for further phosphorylation of the nucleotide to produce the desired phosphorylated AICA ribonucleotide. The selected enzymes were characterized, and conditions were established for two enzymatic cascades. The diphosphorylated AICA ribonucleotide derivative ZDP, synthesized from the cascade EcAPT/AjPPK, was produced with a conversion up to 91 %. The EcAPT/MrPPK cascade yielded ZTP with conversion up to 65 % with ZDP as a side product.

Taylor-made production of pyrimidine nucleoside-5'-monophosphate analogues by highly stabilized mutant uracil phosphoribosyltransferase from Toxoplasma gondii

Nowadays, enzymatic synthesis of nucleotides is an efficient and sustainable alternative to chemical methodologies. In this regard, after the biochemical characterization of wild-type and mutant uracil phosphoribosyltransferases from Toxoplasma gondii (TgUPRT, TgUPRT_2, and TgUPRT₃), TgUPRT₂ was selected as the optimal candidate (69.5 IU mg^-1, UMP synthesis) for structure-guided immobilization onto Ni²⁺ chelate (M_NiUPRT₂) and onto glutaraldehyde-activated microparticles (M_GlUPRT₂). Among resulting derivatives, M_NiUPRT₂3 (6127 IU g^-1_biocat; 92% retained activity; 3-5 fold enhanced stability at 50-60 °C) and M_GlUPRT₂N (3711 IU g^-1_biocat; 27% retained activity; 8-20 fold enhanced stability at 50-60 °C) displayed the best operability. Moreover, the enzymatic synthesis of different pyrimidine NMPs was performed. Finally, the reusability of both derivatives in 5-FUMP synthesis (M_NiUPRT₂3, 80% retained activity after 7 cycles, 5 min; M_GlUPRT₂N, 70% retained activity after 10 cycles, 20 min) was carried out at short times.

A Novel One-Pot Enzyme Cascade for the Biosynthesis of Cladribine Triphosphate

Cladribine triphosphate is the active compound of the anti-cancer and multiple sclerosis drug Mavenclad (cladribine). Biosynthesis of such non-natural deoxyribonucleotides is challenging but important in order to study the pharmaceutical modes of action. In this study, we developed a novel one-pot enzyme cascade for the biosynthesis of cladribine triphosphate, starting with the nucleobase 2Cl-adenine and the generic co-substrate phosphoribosyl pyrophosphate. The cascade is comprised of the three enzymes, namely, adenine phosphoribosyltransferase (APT), polyphosphate kinase (PPK), and ribonucleotide reductase (RNR). APT catalyzes the binding of the nucleobase to the ribose moiety, followed by two consecutive phosphorylation reactions by PPK. The formed nucleoside triphosphate is reduced to the final product 2Cl-deoxyadenonsine triphosphate (cladribine triphosphate) by the RNR. The cascade is feasible, showing comparative product concentrations and yields to existing enzyme cascades for nucleotide biosynthesis. While this study is limited to the biosynthesis of cladribine triphosphate, the design of the cascade offers the potential to extend its application to other important deoxyribonucleotides.

New trends in the biocatalytic production of nucleosidic active pharmaceutical ingredients using 2'-deoxyribosyltransferases

Nowadays, pharmaceutical industry demands competitive and eco-friendly processes for active pharmaceutical ingredients (APIs) manufacturing. In this context, enzyme and whole-cell mediated processes offer an efficient, sustainable and cost-effective alternative to the traditional multi-step and environmentally-harmful chemical processes. Particularly, 2'-deoxyribosyltransferases (NDTs) have emerged as a novel synthetic alternative, not only to chemical but also to other enzyme-mediated synthetic processes. This review describes recent findings in the development and scaling up of NDTs as industrial biocatalysts, including the most relevant and recent examples of single enzymatic steps, multienzyme cascades, chemo-enzymatic approaches, and engineered biocatalysts. Finally, to reflect the inventive and innovative steps of NDT-mediated bioprocesses, a detailed analysis of recently granted patents, with specific focus on industrial synthesis of nucleoside-based APIs, is hereunder presented.

Characterization of NucPNP and NucV involved in the early steps of nucleocidin biosynthesis in Streptomyces calvus

Nucleocidin 1 produced by Streptomyces calvus is one of five characterized natural products containing fluorine. It was discovered in 1956, but its biosynthesis is not yet completely resolved. Recently, the biosynthetic gene cluster of 1 was identified. The nucPNP gene, which was initially annotated as orf206 and encodes a putative purine nucleoside phosphorylase, is essential for nucleocidin production. In this study, we performed in vitro assays and showed NucPNP produced adenine 3 from methylthioadenosine (MTA) 2 and adenosine 4. We also showed the downstream enzyme, NucV annotated as adenine phosphoribosyltransferase (APRT), catalyzes AMP formation from adenine 3 and 5-phospho-α-d-ribose-1-diphosphate (PRPP) 5. However, the catalytic efficiency of NucV was much slower than its homolog ScAPRT involved in the biosynthesis of canonical purine nucleoside in the same strain. These results provide new insights in nucleocidin biosynthesis and could guide future research on organofluorine formation.

Hypoxanthine-Guanine Phosphoribosyltransferase/adenylate Kinase From Zobellia galactanivorans: A Bifunctional Catalyst for the Synthesis of Nucleoside-5'-Mono-, Di- and Triphosphates

In our search for novel biocatalysts for the synthesis of nucleic acid derivatives, we found a good candidate in a putative dual-domain hypoxanthine-guanine phosphoribosyltransferase (HGPRT)/adenylate kinase (AMPK) from Zobellia galactanivorans (ZgHGPRT/AMPK). In this respect, we report for the first time the recombinant expression, production, and characterization of a bifunctional HGPRT/AMPK. Biochemical characterization of the recombinant protein indicates that the enzyme is a homodimer, with high activity in the pH range 6-7 and in a temperature interval from 30 to 80°C. Thermal denaturation experiments revealed that ZgHGPRT/AMPK exhibits an apparent unfolding temperature (Tm) of 45°C and a retained activity of around 80% when incubated at 40°C for 240 min. This bifunctional enzyme shows a dependence on divalent cations, with a remarkable preference for Mg²⁺ and Co²⁺ as cofactors. More interestingly, substrate specificity studies revealed ZgHGPRT/AMPK as a bifunctional enzyme, which acts as phosphoribosyltransferase or adenylate kinase depending upon the nature of the substrate. Finally, to assess the potential of ZgHGPRT/AMPK as biocatalyst for the synthesis of nucleoside-5′-mono, di- and triphosphates, the kinetic analysis of both activities (phosphoribosyltransferase and adenylate kinase) and the effect of water-miscible solvents on enzyme activity were studied.

Structural and functional characterization of thermostable biocatalysts for the synthesis of 6-aminopurine nucleoside-5'-monophospate analogues

The present work describes the functional and structural characterization of adenine phosphoribosyltransferase 2 from Thermus thermophilus HB8 (TtAPRT2). The combination of structural and substrate specificity data provided valuable information for immobilization studies. Dimeric TtAPRT2 was immobilized onto glutaraldehyde-activated MagReSyn®Amine magnetic iron oxide porous microparticles by two different strategies: a) an enzyme immobilization at pH 8.5 to encourage the immobilization process by N-termini (MTtAPRT2A, MTtAPRT2B, MTtAPRT2C) or b) an enzyme immobilization at pH 10.0 to encourage the immobilization process through surface exposed lysine residues (MTtAPRT2D, MTtAPRT2E, MTtAPRT2F). According to catalyst load experiments, MTtAPRT2B (activity: 480 IU g^-1_biocatalyst, activity recovery: 52%) and MTtAPRT2F (activity: 507 IU g^-1_biocatalyst, activity recovery: 44%) were chosen as optimal derivatives. The biochemical characterization studies demonstrated that immobilization process improved the thermostability of TtAPRT2. Moreover, the potential reusability of MTtAPRT2B and MTtAPRT2F was also tested. Finally, MTtAPRT2F was employed in the synthesis of nucleoside-5'-monophosphate analogues.

Purine and pyrimidine salvage pathway in thermophiles: a valuable source of biocatalysts for the industrial production of nucleic acid derivatives

Due to their similarity to natural counterparts, nucleic acid derivatives (nucleobases, nucleosides, and nucleotides, among others) are interesting molecules for pharmaceutical, biomedical, or food industries. For this reason, there is increasing worldwide demand for the development of efficient synthetic processes for these compounds. Chemical synthetic methodologies require numerous protection-deprotection steps and often lead to the presence of undesirable by-products or enantiomeric mixtures. These methods also require harsh operating conditions, such as the use of organic solvents and hazard reagents. Conversely, enzymatic production by whole cells or enzymes improves regio-, stereo-, and enantioselectivity and provides an eco-friendly alternative. Because of their essential role in purine and pyrimidine scavenging, enzymes from purine and pyrimidine salvage pathways are valuable candidates for the synthesis of many different nucleic acid components. In recent years, many different enzymes from these routes, such as nucleoside phosphorylases, nucleoside kinases, 2'-deoxyribosyltransferases, phosphoribosyl transferases, or deaminases, have been successfully employed as biocatalysts in the production of nucleobase, nucleoside, or nucleotide analogs. Due to their great activity and stability at extremely high temperatures, the use of enzymes from thermophiles in industrial biocatalysis is gaining momentum. Thermophilic enzymes not only display unique characteristics such as temperature, chemical, and pH stability but also provide many different advantages from an industrial perspective. This mini-review aims to cover the most representative enzymatic approaches for the synthesis of nucleic acid derivatives. In this regard, we provide detailed comments about enzymes involved in crucial steps of purine and pyrimidine salvage pathways in thermophiles, as well as their biological role, biochemical characterization, active site mechanism, and substrate specificity. In addition, the most interesting synthetic examples reported in the literature are also included.