1. |
Busarakam K,
Bull AT,
Girard G,
Labeda DP,
van Wezel GP,
Goodfellow M,
( 2014 ) Streptomyces leeuwenhoekii sp. nov., the producer of chaxalactins and chaxamycins, forms a distinct branch in Streptomyces gene trees. PMID : 24604690 : DOI : 10.1007/s10482-014-0139-y Abstract >>
A polyphasic study was carried out to establish the taxonomic status of an Atacama Desert isolate, Streptomyces strain C34(T), which synthesises novel antibiotics, the chaxalactins and chaxamycins. The organism was shown to have chemotaxonomic, cultural and morphological properties consistent with its classification in the genus Streptomyces. Analysis of 16S rRNA gene sequences showed that strain C34(T) formed a distinct phyletic line in the Streptomyces gene tree that was very loosely associated with the type strains of several Streptomyces species. Multilocus sequence analysis based on five house-keeping gene alleles underpinned the separation of strain C34(T) from all of its nearest phylogenetic neighbours, apart from Streptomyces chiangmaiensis TA-1(T) and Streptomyces hyderabadensis OU-40(T) which are not currently in the MLSA database. Strain C34(T) was distinguished readily from the S. chiangmaiensis and S. hyderabadensis strains by using a combination of cultural and phenotypic data. Consequently, strain C34(T) is considered to represent a new species of the genus Streptomyces for which the name Streptomyces leeuwenhoekii sp. nov. is proposed. The type strain is C34(T) (= DSM 42122(T) = NRRL B-24963(T)). Analysis of the whole-genome sequence of S. leeuwenhoekii, with 6,780 predicted open reading frames and a total genome size of around 7.86 Mb, revealed a high potential for natural product biosynthesis.
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2. |
Pu JY,
Peng C,
Tang MC,
Zhang Y,
Guo JP,
Song LQ,
Hua Q,
Tang GL,
( 2013 ) Naphthyridinomycin biosynthesis revealing the use of leader peptide to guide nonribosomal peptide assembly. PMID : 23841701 : DOI : 10.1021/ol401549y Abstract >>
Analysis of naphthyridinomycin gene cluster revealed that this antibiotic is generated by nonribosomal peptide synthetase (NRPS) machinery. However, four modules encoded by two genes do not correspond with the structural units in the final product. Genetic and biochemical characterization of the gene cluster suggested that the leader peptide mechanism for the NRPS assembly line was involved in biosynthesis of this tetrahydroisoquinoline alkaloid.
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3. |
Peng C,
Pu JY,
Song LQ,
Jian XH,
Tang MC,
Tang GL,
( 2012 ) Hijacking a hydroxyethyl unit from a central metabolic ketose into a nonribosomal peptide assembly line. PMID : 22586110 : DOI : 10.1073/pnas.1204232109 PMC : PMC3365175 Abstract >>
Nonribosomal peptide synthetases (NRPSs) usually catalyze the biosynthesis of peptide natural products by sequential selection, activation, and condensation of amino acid precursors. It was reported that some fatty acids, �\-ketoacids, and �\-hydroxyacids originating from amino acid metabolism as well as polyketide-derived units can also be used by NRPS assembly lines as an alternative to amino acids. Ecteinascidin 743 (ET-743), naphthyridinomycin (NDM), and quinocarcin (QNC) are three important antitumor natural products belonging to the tetrahydroisoquinoline family. Although ET-743 has been approved as an anticancer drug, the origin of an identical two-carbon (C(2)) fragment among these three antibiotics has not been elucidated despite much effort in the biosynthetic research in the past 30 y. Here we report that two unexpected two-component transketolases (TKases), NapB/NapD in the NDM biosynthetic pathway and QncN/QncL in QNC biosynthesis, catalyze the transfer of a glycolaldehyde unit from ketose to the lipoyl group to yield the glycolicacyl lipoic acid intermediate and then transfer the C(2) unit to an acyl carrier protein (ACP) to form glycolicacyl-S-ACP as an extender unit for NRPS. Our results demonstrate a unique NRPS extender unit directly derived from ketose phosphates through (�\,�]-dihydroxyethyl)-thiamin diphosphate and a lipoyl group-tethered ester intermediate catalyzed by the TKase-ACP platform in the context of NDM and QNC biosynthesis, all of which also highlights the biosynthesis of ET-743. This hybrid system and precursor are distinct from the previously described universal modes involving the NRPS machinery. They exemplify an alternate strategy in hybrid NRPS biochemistry and enrich the diversity of precursors for NRPS combinatorial biosynthesis.
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4. |
Zhang Y,
Huang H,
Chen Q,
Luo M,
Sun A,
Song Y,
Ma J,
Ju J,
( 2013 ) Identification of the grincamycin gene cluster unveils divergent roles for GcnQ in different hosts, tailoring the L-rhodinose moiety. PMID : 23782455 : DOI : 10.1021/ol401253p Abstract >>
The gene cluster responsible for grincamycin (GCN, 1) biosynthesis in Streptomyces lusitanus SCSIO LR32 was identified; heterologous expression of the GCN cluster in S. coelicolor M512 yielded P-1894B (1b) as a predominant product. The �GgcnQ mutant accumulates intermediate 1a and two shunt products 2a and 3a bearing L-rhodinose for L-cinerulose A substitutions. In vitro data demonstrated that GcnQ is capable of iteratively tailoring the two L-rhodinose moieties into L-aculose moieties, supporting divergent roles of GcnQ in different hosts.
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5. |
Dunham NP,
Chang WC,
Mitchell AJ,
Martinie RJ,
Zhang B,
Bergman JA,
Rajakovich LJ,
Wang B,
Silakov A,
Krebs C,
Boal AK,
Bollinger JM,
( 2018 ) Two Distinct Mechanisms for C-C Desaturation by Iron(II)- and 2-(Oxo)glutarate-Dependent Oxygenases: Importance of �\-Heteroatom Assistance. PMID : 29708749 : DOI : 10.1021/jacs.8b01933 PMC : PMC5999578 Abstract >>
Hydroxylation of aliphatic carbons by nonheme Fe(IV)-oxo (ferryl) complexes proceeds by hydrogen-atom (H?) transfer (HAT) to the ferryl and subsequent coupling between the carbon radical and Fe(III)-coordinated oxygen (termed rebound). Enzymes that use H?-abstracting ferryl complexes for other transformations must either suppress rebound or further process hydroxylated intermediates. For olefin-installing C-C desaturations, it has been proposed that a second HAT to the Fe(III)-OH complex from the carbon �\ to the radical preempts rebound. Deuterium (2H) at the second site should slow this step, potentially making rebound competitive. Desaturations mediated by two related l-arginine-modifying iron(II)- and 2-(oxo)glutarate-dependent (Fe/2OG) oxygenases behave oppositely in this key test, implicating different mechanisms. NapI, the l-Arg 4,5-desaturase from the naphthyridinomycin biosynthetic pathway, abstracts H? first from C5 but hydroxylates this site (leading to guanidine release) to the same modest extent whether C4 harbors 1H or 2H. By contrast, an unexpected 3,4-desaturation of l-homoarginine (l-hArg) by VioC, the l-Arg 3-hydroxylase from the viomycin biosynthetic pathway, is markedly disfavored relative to C4 hydroxylation when C3 (the second hydrogen donor) harbors 2H. Anchimeric assistance by N6 permits removal of the C4-H as a proton in the NapI reaction, but, with no such assistance possible in the VioC desaturation, a second HAT step (from C3) is required. The close proximity (?3.5 ?) of both l-hArg carbons to the oxygen ligand in an X-ray crystal structure of VioC harboring a vanadium-based ferryl mimic supports and rationalizes the sequential-HAT mechanism. The results suggest that, although the sequential-HAT mechanism is feasible, its geometric requirements may make competing hydroxylation unavoidable, thus explaining the presence of �\-heteroatoms in nearly all native substrates for Fe/2OG desaturases.
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