Accelerating the discovery of alkyl halide-derived natural products using halide depletion

Engineering the Specificity of Acetyl-CoA Synthetase for Diverse Acyl-CoA Thioester Generation

CoA thioesters are valuable intermediates in numerous biosynthetic routes and metabolic processes. However, diversifying these compounds and their corresponding downstream products hinges on broadening the promiscuity of CoA ligases that produce them or using additional enzymes to functionalize them. Here, the inherent promiscuity of an acyl-CoA ligase from Pseudomonas chlororaphis was probed with carboxylic acids of varying sizes and functionality. The enzyme was engineered to improve its activity with a diverse panel of acyl-CoA thioesters, including halogenated and oxidized acids, that can be used in downstream biosynthetic production strategies. To demonstrate the utility of the engineered enzyme, a subset of the substrates was leveraged for the complete in situ biosynthesis of a small panel of pyrones via a portion of the archetypal polyketide synthase (PKS), 6-deoxyerythronolide B synthase (DEBS). This approach supports probing the promiscuity of polyketide biosynthesis and the diversification of natural product scaffolds.

Transforming monosaccharides: Recent advances in rare sugar production and future exploration

Rare sugars are defined as monosaccharides and their derivatives that do not exist in nature at all or that exist in extremely limited amounts despite being theoretically possible. At present, no comprehensive dogma has been presented regarding how and why these rare sugars have deviated from the naturally selected monosaccharides. In this minireview, we adopt a hypothesis on the origin and evolution of elementary hexoses, previously presented by one of the authors (Hirabayashi, Q Rev Biol, 1996, 71:365-380). In this scenario, monosaccharides, which constitute various kinds of glycans in nature, are assumed to have been generated by formose reactions on the prebiotic Earth (chemical evolution era). Among them, the most stable hexoses, i.e., fructose, glucose, and mannose remained accumulated. After the birth of life, the "chemical origin" saccharides thus survived were transformed into a variety of "bricolage products", which include galactose and other recognition saccharides like fucose and sialic acid through the invention of diverse metabolic pathways (biological evolution era). The remaining monosaccharides that have deviated from this scenario are considered rare sugars. If we can produce rare sugars as we wish, it is expected that various more useful biomaterials will be created by using them as raw materials. Thanks to the pioneering research of the Izumori group in the 1990's, and to a few other investigations by other groups, almost all monosaccharides including l-sugars can now be produced by combining both chemical and enzymatic approaches. After briefly giving an overview of the origin of elementary hexoses and the current state of the rare sugar production, we will look ahead to the next generation of monosaccharide research which also targets glycosides including disaccharides.

Expanding the Diversity of the Cyanobacterial Dialkylresorcinol Bartoloside Family

The cyanobacterial dialkylresorcinol bartolosides were initially reported to feature glycosylated and halogenated moieties. Later, biosynthetic and in vitro studies showed that the chlorinated alkyl chains are utilized for a nucleophilic substitution with free fatty acid carboxylates from primary metabolism, generating bartoloside esters. Here, we applied a workflow based on PCR screening coupled to LC-HRESIMS and molecular network analysis with the aim of discovering additional bartoloside diversity. We report the annotation of 27 bartoloside and bartoloside ester derivatives, including the characterization of two new bartolosides, underlining the breadth of structures generated by bartoloside biosynthetic pathways. Some of the herein reported bartolosides feature hydroxylation in their side chains, a modification that has not been associated with this metabolite family.

Chemo-enzymatic total synthesis: current approaches toward the integration of chemical and enzymatic transformations

A steadily increasing number of reports have been published on chemo-enzymatic synthesis methods that integrate biosynthetic enzymatic transformations with chemical conversions. This review focuses on the total synthesis of natural products and classifies the enzymatic reactions into three categories. The total synthesis of five natural products: cotylenol, trichodimerol, chalcomoracin, tylactone, and saframycin A, as well as their analogs, is outlined with an emphasis on comparing these chemo-enzymatic syntheses with the corresponding natural biosynthetic pathways.

Vanadium haloperoxidases as noncanonical terpene synthases

Vanadium-dependent haloperoxidases (VHPOs) are a unique family of enzymes that utilize vanadate, an aqueous halide ion, and hydrogen peroxide to produce an electrophilic halogen species that can be incorporated into electron rich organic substrates. This halogen species can react with terpene substrates and trigger halonium-induced cyclization in a manner reminiscent of class II terpene synthases. While not all VHPOs act in this capacity, several notable examples from algal and actinobacterial species have been characterized to catalyze regio- and enantioselective reactions on terpene and meroterpenoid substrates, resulting in complex halogenated cyclic terpenes through the action of single enzyme. In this article, we describe the expression, purification, and chemical assays of NapH4, a difficult to express characterized VHPO that catalyzes the chloronium-induced cyclization of its meroterpenoid substrate.