HCN production and hydroxynitrile lyase: a natural activity in plants and a renewed biotechnological interest

The Paradox of Antimalarial Terpenoid Isonitrile Biosynthesis Explained. Proposal of Cyanoformate as an NC Delivery Vector

Marine sponge diterpenoid isonitriles are exceptional nitrogenous natural products that exhibit antiplasmodial activity. Their biosynthesis presents a biosynthetic puzzle: how do the elements of NC engage terpenyl carbocations in isoprenoid secondary metabolism, and what is the biosynthetic precursor of the NC group? Cyanoformic acid (NC-COOH, B1) is proposed as a plausible delivery vehicle of NC that resolves a paradox in the commonly held proposition that an inorganic cyanide anion, CN-, terminates terpenoid isonitrile (TI) biosynthesis. DFT calculations of NC-COOH and its conjugate base, cyanoformate, NC-COO- (B2), support high nucleophilicity at N and explain bond-forming constitutionality: attack at N and formation of an isonitrile over its nitrile isomer. TI biogenesis is compared to the cyanoformamide-containing ceratamines that arise from oxidation of a terminal N-Gly amide precursor. A unifying model links C-NC vs C-CN bond formation and places Gly at the center of both biosynthetic schemes.

Cyanide content, nutrient composition, physicochemical properties and sensory quality of flaxseed oil bodies prepared from flaxseeds (Linum usitatissimum L.) treated with different heat treatment methods

Flaxseeds (Linum usitatissimum L.) were pre-treated with different heat treatment methods including steaming (100 °C for 10 min, 20 min or 30 min), roasting (120 °C for 10 min, 20 min or 30 min) and microwave (560 W for 1 min, 2 min or 3 min). Flaxseed oil bodies were prepared from the flaxseeds with and without heat treatment, and the cyanide content, yield rate, nutritional composition, physico properties, rheological behavior, and sensory characteristic were evaluated. These three types of heat treatment methods could effectively reduce the content (1.87-13.98 mg/kg) of toxic cyanide in flaxseed oil bodies. In addition, compared with the flaxseed oil bodies in steaming and roasting treated groups, the flaxseed oil bodies in microwave treated group exhibited higher yield rate (36.37-39.71 %), lower level of lipid oxidation (peroxide value, 6.10-7.10 mmol/kg lipid; thiobarbituric acid reactive substances, 1.99-2.20 mg MDA/kg lipid), higher content of polyunsaturated fatty acids (PUFAs, 63.33-64.22 %), better viscoelasticity, and better appearance color. Therefore, microwave treatment at 560 W with less than 3 min is a suitable preheating method of flaxseeds, thus improving the quality of the obtaind oil bodies.

Catalytically active inclusion bodies (CatIBs) induced by terminally attached self-assembling coiled-coil domains: To enhance the stability of (R)-hydroxynitrile lyase

The catalytically-active inclusion bodies (CatIBs) represent a promising strategy for immobilizing enzyme without additional carriers and chemicals, which has aroused great attention in academic and industrial communities. In this work, we discovered two natural parallel right-handed coiled-coil tetramer peptides from PDB database by a structural mining strategy. The two self-assembling peptides, NSPdoT from rotavirus and HVdoT from human Vasodilator-stimulated phosphoprotein, efficiently induced the CatIBs formation of a (R)-Hydroxynitrile lyase from Arabidopsis thaliana (AtHNL) in Escherichia coli cells. This is convenient to simultaneously purify and immobilize the target proteins as biocatalysts. As expected, HVdoT-AtHNL and NSPdoT-AtHNL possessed drastically increased tolerance toward lower pH values, which will be very critical to synthesize cyanohydrins under acidic condition for suppressing the non-enzymatic side reaction. In addition. AtHNL-CatIBs are produced at high yield in host cells as bioactive microparticles, which exhibited high thermal and pH stabilities. Therefore, the CatIBs method represent a promising application for the immobilization of enzymes in the biocatalysis field.

Catalytic Promiscuity of Galactose Oxidase: A Mild Synthesis of Nitriles from Alcohols, Air, and Ammonia

We report an unprecedented catalytically promiscuous activity of the copper-dependent enzyme galactose oxidase. The enzyme catalyses the one-pot conversion of alcohols into the related nitriles under mild reaction conditions in ammonium buffer, consuming ammonia as the source of nitrogen and dioxygen (from air at atmospheric pressure) as the only oxidant. Thus, this green method does not require either cyanide salts, toxic metals, or undesired oxidants in stoichiometric amounts. The substrate scope of the reaction includes benzyl and cinnamyl alcohols as well as 4- and 3-pyridylmethanol, giving access to valuable chemical compounds. The oxidation proceeds through oxidation from alcohol to aldehyde, in situ imine formation, and final direct oxidation to nitrile.

Enantioselective synthesis of cyanohydrins catalysed by hydroxynitrile lyases - a review

The first enantioselective synthesis was the selective addition of cyanide to benzaldehyde catalysed by a hydroxynitrile lyase (HNL). Since then these enzymes have been developed into a reliable tool in organic synthesis. HNLs to prepare either the (R)- or the (S)-enantiomer of the desired cyanohydrin are available and a wide variety of reaction conditions can be applied. As a result of this, numerous applications of these enzymes in organic synthesis have been described. Here the examples of the last decade are summarised, the enzyme catalysed step is discussed and the follow-up chemistry is shown. This proves HNLs to be part of main stream organic synthesis. Additionally the newest approaches via immobilisation and reaction engineering are introduced.

Enzyme discovery beyond homology: a unique hydroxynitrile lyase in the Bet v1 superfamily

Homology and similarity based approaches are most widely used for the identification of new enzymes for biocatalysis. However, they are not suitable to find truly novel scaffolds with a desired function and this averts options and diversity. Hydroxynitrile lyases (HNLs) are an example of non-homologous isofunctional enzymes for the synthesis of chiral cyanohydrins. Due to their convergent evolution, finding new representatives is challenging. Here we show the discovery of unique HNL enzymes from the fern Davallia tyermannii by coalescence of transcriptomics, proteomics and enzymatic screening. It is the first protein with a Bet v1-like protein fold exhibiting HNL activity, and has a new catalytic center, as shown by protein crystallography. Biochemical properties of D. tyermannii HNLs open perspectives for the development of a complementary class of biocatalysts for the stereoselective synthesis of cyanohydrins. This work shows that systematic integration of -omics data facilitates discovery of enzymes with unpredictable sequences and helps to extend our knowledge about enzyme diversity.