Staurosporine isolated fromThe subsequent oxidative decarboxylation reaction is also discussed based on the crystal structure. Our crystallographic study shows the first crystal structures of enzymes involved in formation of the indolocarbazole core and provides valuable insights into the process of staurosporine biosynthesis, combinatorial biosynthesis of indolocarbazoles, and the diversity of cytochrome P450 chemistry.heme ͉ staurosporine ͉ rebeccamycin ͉ secondary metabolism S taurosporine and rebeccamycin (Fig. 1A) are natural products that have attracted much attention because of their strong inhibitory activity for protein kinase or DNA topoisomerase, which makes them therapeutically important anticancer agents. These natural products are members of a family of indolocarbazole alkaloids which have a similar structure, including an indole[2,3-a]carbazole core with a C-N linkage to a sugar moiety.The staurosporine biosynthetic gene cluster from Streptomyces sp. TP-A0274 and the rebeccamycin biosynthetic gene cluster from Lechevalieria aerocolonigenes (39243; American Type Culture Collection, Manassas, VA) have been cloned and characterized. The staurosporine biosynthetic gene cluster consists of 15 ORFs spanning 22 kb (1), and the rebeccamycin biosynthetic gene cluster consists of 11 genes spanning 17 kb (2, 3). Gene disruption and/or heterologous gene expression experiments revealed that four genes (staO, staD, staP, and staC in Streptomyces sp. TP-A0274 and the homologous genes rebO, rebD, rebP, and rebC in L. aerocolonigenes) are responsible for the biosynthesis of the indolocarbazole skeleton (2, 3). In staurosporine biosynthesis, StaO initiates the synthesis by catalyzing the reaction of tryptophan to the imine form of indole-3-pyruvic acid (IPA imine), and StaD then catalyzes the coupling of two molecules of IPA imine to yield chromopyrrolic acid (CPA). Finally, the key skeleton structure referred to as the indolocarbazole core is constructed through the following two oxidation steps by StaP and StaC (2, 4) (Fig. 1B).StaP (CYP245A1) is a member of the cytochrome P450 family (5), which includes heme enzymes involved in steroid hormone biosynthesis, drug metabolism, and many other physiologically

Ultraviolet-protective compounds, such as mycosporine-like amino acids (MAAs) and related gadusols produced by some bacteria, fungi, algae, and marine invertebrates, are critical for the survival of reef-building corals and other marine organisms exposed to high-solar irradiance. These compounds have also been found in marine fish, where their accumulation is thought to be of dietary or symbiont origin. In this study, we report the unexpected discovery that fish can synthesize gadusol de novo and that the analogous pathways are also present in amphibians, reptiles, and birds. Furthermore, we demonstrate that engineered yeast containing the fish genes can produce and secrete gadusol. The discovery of the gadusol pathway in vertebrates provides a platform for understanding its role in these animals, and the possibility of engineering yeast to efficiently produce a natural sunscreen and antioxidant presents an avenue for its large-scale production for possible use in pharmaceuticals and cosmetics.DOI: http://dx.doi.org/10.7554/eLife.05919.001

Sedoheptulose 7-phosphate cyclases are enzymes that utilize the pentose phosphate pathway intermediate, sedoheptulose 7-phosphate, to generate cyclic precursors of many bioactive natural products, such as the antidiabetic drug acarbose, the crop protectant validamycin, and the natural sunscreens mycosporine-like amino acids. These proteins are phylogenetically related to the dehydroquinate (DHQ) synthases from the shikimate pathway, and are part of the more recently recognized superfamily of sugar phosphate cyclases, which includes DHQ synthases, aminoDHQ synthases and 2-deoxy-scyllo-inosose synthases. Through genome mining and biochemical studies, we identified yet another subset of DHQS-like proteins in the actinomycete Actinosynnema mirum and the myxobacterium Stigmatella aurantiaca DW4/3–1. These enzymes catalyze the conversion of sedoheptulose 7-phosphate to 2-epi-valiolone, which is predicted to be an alternative precursor for aminocyclitol biosynthesis. Comparative bioinformatics and biochemical analyses of these proteins with 2-epi-5-epi-valiolone synthases (EEVS) and desmethyl-4-deoxygadusol synthases (DDGS) provided further insights into their genetic diversity, conserved amino acid sequences, and plausible catalytic mechanisms. The results further highlight the uniquely diverse DHQS-like sugar phosphate cyclases, which may provide new tools for chemoenzymatic, stereospecific synthesis of various cyclic molecules.

Lactazole A is a cryptic thiopeptide from Streptomyces lactacystinaeus, encoded by a compact 9.8 kb biosynthetic gene cluster. Here, we establish a platform for in vitro biosynthesis of lactazole A, referred to as the FIT-Laz system, via a combination of the flexible in vitro translation (FIT) system with recombinantly produced lactazole biosynthetic enzymes. Systematic dissection of lactazole biosynthesis reveals remarkable substrate tolerance of the biosynthetic enzymes and leads to the development of the minimal lactazole scaffold, a construct requiring only 6 post-translational modifications for macrocyclization. Efficient assembly of such minimal thiopeptides with FIT-Laz opens access to diverse lactazole analogs with 10 consecutive mutations, 14- to 62-membered macrocycles, and 18 amino acid-long tail regions, as well as to hybrid thiopeptides containing non-proteinogenic amino acids. This work suggests that the minimal lactazole scaffold is amenable to extensive bioengineering and opens possibilities to explore untapped chemical space of thiopeptides.

Chromopyrrolic acid (CPA) oxidation by cytochrome P450 StaP is a key process in the biosynthesis of antitumor drugs (Onaka, H.; Taniguchi, S.; Igarashi, Y.; Furumai, T. Biosci. Biotechnol. Biochem. 2003, 67, 127-138), which proceeds by an unusual C-C bond coupling. Additionally, because CPA is immobilized by a hydrogen-bonding array, it is prohibited from undergoing direct reaction with Compound I, the active species of P450. As such, the mechanism of P450 StaP poses a puzzle. In the present Article, we resolve this puzzle by combination of theory, using QM/MM calculations, and experiment, using crystallography and reactivity studies. Theory shows that the hydrogen-bonding machinery of the pocket deprotonates the carboxylic acid groups of CPA, while the nearby His(250) residue and the crystal waters, Wat(644) and Wat(789), assist the doubly deprotonated CPA to transfer electron density to Compound I; hence, CPA is activated toward proton-coupled electron transfer that sets the entire mechanism in motion. The ensuing mechanism involves a step of C-C bond formation coupled to a second electron transfer, four proton-transfer and tautomerization steps, and four steps where Wat(644) and Wat(789) move about and mediate these events. Experiments with the dichlorinated substrate, CCA, which expels Wat(644), show that the enzyme loses its activity. H250A and H250F mutations of P450 StaP show that His(250) is important, but in its absence Wat(644) and Wat(789) form a hydrogen-bonding diad that mediates the transformation. Thus, the water diad emerges as the minimal requisite element that endows StaP with function. This highlights the role of water molecules as biological catalysts that transform a P450 to a peroxidase-type (Derat, E.; Shaik, S. J. Am. Chem. Soc. 2006, 128, 13940-13949).

Although >100 thiopeptides have been discovered, the number of validated gene clusters involved in their biosynthesis is lagging. We use genome mining to identify a silent thiopeptide biosynthetic gene cluster responsible for biosynthesis of lactazoles. Lactazoles are structurally unique thiopeptides with a 32-membered macrocycle and a 2-oxazolyl-6-thiazolyl pyridine core. We demonstrate that lactazoles originate from the simplest cluster, containing only six unidirectional genes (lazA to lazF). We show that lazC is involved in the macrocyclization process, leading to central pyridine moiety formation. Substitution of the endogenous promoter with a strong promoter results in an approximately 30-fold increase in lactazole A production and mutagenesis of lazC precursor gene in production of two analogs. Lactazoles do not exhibit antimicrobial activity but may modulate signaling cascades triggered by bone morphogenetic protein. Our approach facilitates the production of a more diverse set of thiopeptide structures, increasing the semisynthetic repertoire for use in drug development.

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Eight novel 5-alkyl-1,2,3,4-tetrahydroquinolines (5aTHQs) bearing different side chains have been isolated from a combined culture of Streptomyces nigrescens HEK616 and Tsukamurella pulmonis TP-B0596. The chemical structures including the absolute configuration were elucidated by spectroscopic analysis and total synthesis. 5aTHQs inhibited the growth of wild-type fission yeast while only weakly inhibiting the growth of several mutant strains synthesizing premature ergosterol. These results demonstrate that 5aTHQs are novel antifungals that may target cell membranes.