Isolation, structural elucidation and biosynthesis of 3-hydroxy-6-dimethylallylindolin-2-one, a novel prenylated indole derivative from Actinoplanes missouriensis

Abstract

Many prenylated indole derivatives are widely distributed in nature. Recently, two Streptomyces prenyltransferases, IptA and its homolog SCO7467, were identified in the biosynthetic pathways for 6-dimethylallylindole (DMAI)-3-carbaldehyde and 5-DMAI-3-acetonitrile, respectively. Here, we isolated a novel prenylated indole derivative, 3-hydroxy-6-dimethylallylindolin (DMAIN)-2-one, based on systematic purification of metabolites from a rare actinomycete, Actinoplanes missouriensis NBRC 102363. The structure of 3-hydroxy-6-DMAIN-2-one was determined by HR-MS and NMR analyses. We found that A. missouriensis produced not only 3-hydroxy-6-DMAIN-2-one but also 6-dimethylallyltryptophan (DMAT) and 6-DMAI when grown in PYM (peptone-yeast extract-MgSO4) medium. We searched the complete genome of A. missouriensis for biosynthesis genes of these compounds and found a gene cluster composed of an iptA homolog (AMIS_22580, named iptA-Am) and a putative tryptophanase gene (AMIS_22590, named tnaA-Am). We constructed a tnaA-Am-deleted (ΔtnaA-Am) strain and found that it produced 6-DMAT but did not produce 6-DMAI or 3-hydroxy-6-DMAIN-2-one. Exogenous addition of 6-DMAI to mutant ΔtnaA-Am resulted in the production of 3-hydroxy-6-DMAIN-2-one. Furthermore, in vitro enzyme assays using recombinant proteins produced by Escherichia coli demonstrated that 6-DMAI was synthesized from tryptophan and dimethylallyl pyrophosphate in the presence of both IptA-Am and TnaA-Am, and that IptA-Am preferred tryptophan to indole as the substrate. From these results, we concluded that the iptA-Am-tnaA-Am gene cluster is responsible for the biosynthesis of 3-hydroxy-6-DMAIN-2-one. Presumably, tryptophan is converted into 6-DMAT by IptA-Am and 6-DMAT is then converted into 6-DMAI by TnaA-Am. 6-DMAI appears to be converted into 3-hydroxy-6-DMAIN-2-one by the function of some unknown oxidases in A. missouriensis.

The secondary metabolites of rare actinomycetes: chemistry and bioactivity

“…9). 69 From a bioactivity-guided approach, an antifungal metabolite, 5-hydroxyl-5-methyl-2-hexenoic acid (221), was found from Actinoplanes sp. HBDN08 obtained from a soil sample collected in Harbin, China.…”

Involvement of β‐Alkylation Machinery and Two Sets of Ketosynthase‐Chain‐Length Factors in the Biosynthesis of Fogacin Polyketides in Actinoplanes missouriensis

“…It shows interesting morphological features and forms sporangia containing motile sporangiospores . We have shown that this strain produces several secondary metabolites, including alkyl‐ O ‐dihydrogeranyl‐methoxyhydroquinones and 3‐hydroxy‐6‐dimethylallylindolin‐2‐one . However, analysis of the secondary metabolite biosynthetic gene clusters of A. missouriensis by antiSMASH indicated that this strain had at least 10 secondary metabolite biosynthetic gene clusters .…”

Characterisation of 6-DMATSMofrom Micromonospora olivasterospora leading to identification of the divergence in enantioselectivity, regioselectivity and multiple prenylation of tryptophan prenyltransferases

“…SN-593 functions as a 6-DMATS and is involved in the biosynthesis of 6-dimethylallylindole-3-carbaldehyde. 18 Three IptA orthologues, IptA Am from Actinoplanes missouriensis, 19 6-DMATS Sa from Streptomyces ambofaciens (S. ambofaciens), and 6-DMATS Sv from S. violaceusniger have been recently identified and characterised. 20 SCO7467 from S. coelicolor A3(2) belongs to a gene cluster being responsible for the biosynthesis of 5-dimethylallylindole-3-acetonitrile and the encoded protein acts as a 5-DMATS (5-DMATS Sc ).…”