Search

Main observation and conclusion: The enzyme AbyU catalyses a Diels‐Alder (DA) reaction during abyssomicin C biosynthesis. In this study, AbyU is shown to convert the native substrate of another Diels‐Alderase (DAase), AbmU, to a new abyssomicin derivative, abyssomicin 7. Abyssomicin 7 is a diastereomer of the AbmU‐derived, abyssomicin 6. Using structural analyses and site‐directed mutagenesis, we unveil the molecular basis for production of abyssomicin 7, instead of abyssomicin 6, within the AbyU active site. [ABSTRACT FROM AUTHOR]

β-Carboline alkaloids (βCs), with tricyclic pyrido[3,4- b]indole rings, have important pharmacological and therapeutic value. In the biosynthesis of βCs, the Pictet-Spengler (PS) cyclization reaction is responsible for the formation of ring structures. McbB is one of a few enzymes that are known to catalyse PS cyclization. It can also catalyse decarboxylation and oxidation. Here, the expression, crystallization and preliminary data analysis of McbB are reported. The crystals diffracted to 2.10 Å resolution and belonged to the monoclinic space group P21, with unit-cell parameters a = 66.06, b = 85.48, c = 106.19 Å, α = 90.00, β = 106.77, γ = 90.00°. These results provide a basis for solving the crystal structure and elucidating the catalytic mechanism for McbB. [ABSTRACT FROM AUTHOR]

The article focuses on the study on the enzyme catalyzing the β-carboline (βCs) skeleton construction in marinacarboline biosynthetic pathway. The study involves the isolation of marinacarbolines A-D and 1-acetyl-βCs from the deep South China Sea-derived Marinactinospora thermotolerans. The study reveals that McbB plays an important role in βCs skeleton assembly and that effects of McbA and McbC knockout are consistent with CoA ligase inactivation.

Highlights: [•] The CO-difference spectra of HmtT and HmtN show absorbance at 450nm. [•] Instead of lying at the entrance of the active site, the exceptionally long F–G loop of HmtT takes a highly unusual conformation and extends deep into the active site. As a result, both F and G helices of HmtT are kinked. [•] The F/G helices adopt distinctive orientations in HmtT and HmtN, which may play a role in distinguishing subtle differences on the highly homologous substrates. [ABSTRACT FROM AUTHOR]

Four new indolo-sesquiterpenes - dixiamycins A ( 1) and B ( 2), oxiamycin ( 3), and chloroxiamycin ( 4) - were isolated from a marine-derived Actinomycete and characterized, together with the known compound xiamycin A ( 5). Dixiamycins A ( 1) and B ( 2) are the first examples of atropisomerism of naturally occurring N-N-coupled atropo-diastereomers, with a dimeric indolo-sesquiterpene skeleton and a stereogenic N-N axis between sp3-hybridized nitrogen atoms. Solution TDDFT ECD calculations were utilized to ascertain the axial chirality of 1 and 2, and rotational barriers and transitions states of the inversion were calculated. Oxiamycin ( 3) contains a seven-membered 2,3,4,5-tetrahydrooxepine ring. The two dimeric compounds 1 and 2 showed better antibacterial activities than the monomers 3- 5. [ABSTRACT FROM AUTHOR]

Two new cytochalasins, 18-deoxycytochalasin Q ( 1) and 21- O-deacetylcytochalasin Q ( 2), together with four known analogues, cytochalasin Q ( 3), 19,20-epoxycytochalasin Q ( 4), 21- O-deacetyl-19,20-epoxycytochalasin Q ( 5), and cytochalasin D ( 6), were isolated from the fungus Xylaria sp. SCSIO156 originated from the South China Sea marine sediment. The structures of 1 and 2 were elucidated by MS and 1D- and 2D-NMR data analyses, and comparison with known compounds. The known compounds 3- 6 were identified by comparison of their MS and NMR data with those reported in the literature. In the in vitro antitumor assay, compounds 2- 6 showed mild cytotoxicity against three tumor cell lines (MCF-7, SF-268, and NCI-H460). [ABSTRACT FROM AUTHOR]