4-Deoxy-l-erythro-5-hexoseulose Uronate (DEH) and DEH Reductase: Key Molecule and Enzyme for the Metabolism and Utilization of Alginate

4-Deoxy-l-erythro-5-hexoseulose uronate (DEH), DEH reductase, and alginate lyase have key roles in the metabolism of alginate, a promising carbon source in brown macroalgae for biorefinery. In contrast to the widely reviewed alginate lyase, DEH and DEH reductase have not been previously reviewed. Here, we summarize the current understanding of DEH and DEH reductase, with emphasis on (i) the non-enzymatic and enzymatic formation and structure of DEH and its reactivity to specific amino groups, (ii) the molecular identification, classification, function, and structure, as well as the structural determinants for coenzyme specificity of DEH reductase, and (iii) the significance of DEH for biorefinery. Improved understanding of this and related fields should lead to the practical utilization of alginate for biorefinery.

Identification and characterization of piperine synthase from black pepper, Piper nigrum L.

Black pepper (Piper nigrum L.) is the world’s most popular spice and is also used as an ingredient in traditional medicine. Its pungent perception is due to the interaction of its major compound, piperine (1-piperoyl-piperidine) with the human TRPV-1 or vanilloid receptor. We now identify the hitherto concealed enzymatic formation of piperine from piperoyl coenzyme A and piperidine based on a differential RNA-Seq approach from developing black pepper fruits. This enzyme is described as piperine synthase (piperoyl-CoA:piperidine piperoyl transferase) and is a member of the BAHD-type of acyltransferases encoded by a gene that is preferentially expressed in immature fruits. A second BAHD-type enzyme, also highly expressed in immature black pepper fruits, has a rather promiscuous substrate specificity, combining diverse CoA-esters with aliphatic and aromatic amines with similar efficiencies, and was termed piperamide synthase. Recombinant piperine and piperamide synthases are members of a small gene family in black pepper. They can be used to facilitate the microbial production of a broad range of medicinally relevant aliphatic and aromatic piperamides based on a wide array of CoA-donors and amine-derived acceptors, offering widespread applications.

Recent Advances in the Biosynthesis of Carbazoles Produced by Actinomycetes

Structurally diverse carbazole alkaloids are valuable due to their pharmaceutical properties and have been isolated from nature. Experimental knowledge on carbazole biosynthesis is limited. The latest development of in silico analysis of the biosynthetic gene clusters for bacterial carbazoles has allowed studies on the biosynthesis of a carbazole skeleton, which was established by sequential enzyme-coupling reactions associated with an unprecedented carbazole synthase, a thiamine-dependent enzyme, and a ketosynthase-like enzyme. This review describes the carbazole biosynthetic mechanism, which includes a key step in enzymatic formation of a tricyclic carbazole skeleton, followed by modifications such as prenylation and hydroxylation in the skeleton.

Organic thiocyanates - glucosinolate enzymatic degradation products or artefacts of the isolation procedure?

Glucosinolates are abundant in plants of the order Brassicales, and they are degraded by myrosinases into various organic breakdown products: isothiocyanates, thiocyanates, nitriles, etc., depending on their structure, conditions of hydrolysis, the presence of certain protein cofactors. Their most common hydrolysis products are isothiocyanates, while simple nitriles, epithionitriles, and thiocyanates are produced occasionally. Organic thiocyanates are described from a very limited number of Brassicales taxa. Up to now benzyl, (4-hydroxyphenyl)methyl, (4-methoxyphenyl)methyl, 4- methylthiobutyl, and allyl thiocyanates were reported as products of glucosinolates autolysis. The present review summarizes the knowledge on the mechanism of organic thiocyanate formation from the corresponding thioglucosides. The enzymatic formation of organic thiocyanates is believed to be enabled by thiocyanate-forming protein (TFP), but they could be formed via metabolic routes that do not involve TFP. All of the reported thiocyanates are produced from stable (carbo)cationic species that allow an isomerization of an isothiocyanate to thiocyanate, and vice versa. Although the possibility that thiocyanates can be biosynthesized in plats under certain conditions cannot be dismissed, allyl thiocyanate can be a thermal isomerization artefact of the original isothiocyanate that is formed in the heated zones of the gas chromatograph, while other thiocyanates could form in an aqueous medium via heterolytic dissociation to ambident nucleophilic SCN- and its recapture. One should always be aware of this analytical shortcoming when concluding on the presence and quantity of these specific (iso)thiocyanantes in the analyzed sample.

Enzymatic formation of consecutive thymine–HgII–thymine base pairs by DNA polymerases

Ten consecutive T–HgII–T base pairs were successfully formed by DNA polymerase-catalyzed primer extension reactions.