7 research outputs found
Table_1.doc
<p>AdpA, an AraC/XylS family protein, had been proved as a key regulator for secondary metabolism and morphological differentiation in Streptomyces griseus. Here, we identify AdpA<sub>ch</sub>, an ortholog of AdpA, as a “higher level” pleiotropic regulator of natamycin biosynthesis with bidirectional regulatory ability in Streptomyces chattanoogensis L10. DNase I footprinting revealed six AdpA<sub>ch</sub>-binding sites in the scnRI–scnRII intergenic region. Further analysis using the xylE reporter gene fused to the scnRI–scnRII intergenic region of mutated binding sites demonstrated that the expression of scnRI and scnRII was under the control of AdpA<sub>ch</sub>. AdpA<sub>ch</sub> showed a bi-stable regulatory ability where it firstly binds to the Site C and Site D to activate the transcription of the two pathway-specific genes, scnRI and scnRII, and then binds to other sites where it acts as an inhibitor. When Site A and Site F were mutated in vivo, the production of natamycin was increased by 21% and 25%, respectively. These findings indicated an autoregulatory mechanism where AdpA<sub>ch</sub> serves as a master switch with bidirectional regulation for natamycin biosynthesis.</p
Image_1_Substrate Specificity of Acyltransferase Domains for Efficient Transfer of Acyl Groups.TIF
<p>Acyltransferase domains (ATs) of polyketide synthases (PKSs) are critical for loading of acyl groups on acyl carrier protein domains (A) via self- and trans-acylation reactions, to produce structurally diverse polyketides. However, the interaction specificity between ATs and unusual acyl units is rarely documented. In Streptomycestsukubaensis YN06, we found that AT4<sub>FkbB</sub> [an AT in the fourth module of tacrolimus (FK506) PKS] transferred both allylmalonyl (allmal) and emthylmalonyl (ethmal) units to ACPs, which was supposed responsible for the production of both FK506 and its analog FK520, respectively. Mutations of five residues in AT4<sub>FkbB</sub> (Q119A, L185I-V186D-V187T, and F203L) caused decreased efficiency of allmal transfer, but a higher ratio of ethmal transfer, supposedly due to less nucleophilic attacks between Ser599 in the active site of AT4<sub>FkbB</sub> and the carbonyl carbon in the allmal unit, as observed from molecular dynamics simulations. Furthermore, reverse mutations of these five residues in ethmal-specific ATs to the corresponding residues of AT4<sub>FkbB</sub> increased its binding affinity to allmal-CoA. Among these residues, Val187 of AT4<sub>FkbB</sub> mainly contributed to allmal recognition, and V187K mutant produced less FK520 than wild type. Our findings thus suggested that five critical residues within AT4<sub>FkbB</sub> were important for AT functionality in polyketide extension and potentially for targeting biosynthesis by generating desirable products and eliminating undesirable analogs.</p
Image_3_Substrate Specificity of Acyltransferase Domains for Efficient Transfer of Acyl Groups.TIF
<p>Acyltransferase domains (ATs) of polyketide synthases (PKSs) are critical for loading of acyl groups on acyl carrier protein domains (A) via self- and trans-acylation reactions, to produce structurally diverse polyketides. However, the interaction specificity between ATs and unusual acyl units is rarely documented. In Streptomycestsukubaensis YN06, we found that AT4<sub>FkbB</sub> [an AT in the fourth module of tacrolimus (FK506) PKS] transferred both allylmalonyl (allmal) and emthylmalonyl (ethmal) units to ACPs, which was supposed responsible for the production of both FK506 and its analog FK520, respectively. Mutations of five residues in AT4<sub>FkbB</sub> (Q119A, L185I-V186D-V187T, and F203L) caused decreased efficiency of allmal transfer, but a higher ratio of ethmal transfer, supposedly due to less nucleophilic attacks between Ser599 in the active site of AT4<sub>FkbB</sub> and the carbonyl carbon in the allmal unit, as observed from molecular dynamics simulations. Furthermore, reverse mutations of these five residues in ethmal-specific ATs to the corresponding residues of AT4<sub>FkbB</sub> increased its binding affinity to allmal-CoA. Among these residues, Val187 of AT4<sub>FkbB</sub> mainly contributed to allmal recognition, and V187K mutant produced less FK520 than wild type. Our findings thus suggested that five critical residues within AT4<sub>FkbB</sub> were important for AT functionality in polyketide extension and potentially for targeting biosynthesis by generating desirable products and eliminating undesirable analogs.</p
Table_1_Substrate Specificity of Acyltransferase Domains for Efficient Transfer of Acyl Groups.DOC
<p>Acyltransferase domains (ATs) of polyketide synthases (PKSs) are critical for loading of acyl groups on acyl carrier protein domains (A) via self- and trans-acylation reactions, to produce structurally diverse polyketides. However, the interaction specificity between ATs and unusual acyl units is rarely documented. In Streptomycestsukubaensis YN06, we found that AT4<sub>FkbB</sub> [an AT in the fourth module of tacrolimus (FK506) PKS] transferred both allylmalonyl (allmal) and emthylmalonyl (ethmal) units to ACPs, which was supposed responsible for the production of both FK506 and its analog FK520, respectively. Mutations of five residues in AT4<sub>FkbB</sub> (Q119A, L185I-V186D-V187T, and F203L) caused decreased efficiency of allmal transfer, but a higher ratio of ethmal transfer, supposedly due to less nucleophilic attacks between Ser599 in the active site of AT4<sub>FkbB</sub> and the carbonyl carbon in the allmal unit, as observed from molecular dynamics simulations. Furthermore, reverse mutations of these five residues in ethmal-specific ATs to the corresponding residues of AT4<sub>FkbB</sub> increased its binding affinity to allmal-CoA. Among these residues, Val187 of AT4<sub>FkbB</sub> mainly contributed to allmal recognition, and V187K mutant produced less FK520 than wild type. Our findings thus suggested that five critical residues within AT4<sub>FkbB</sub> were important for AT functionality in polyketide extension and potentially for targeting biosynthesis by generating desirable products and eliminating undesirable analogs.</p
Image_4_Substrate Specificity of Acyltransferase Domains for Efficient Transfer of Acyl Groups.TIF
<p>Acyltransferase domains (ATs) of polyketide synthases (PKSs) are critical for loading of acyl groups on acyl carrier protein domains (A) via self- and trans-acylation reactions, to produce structurally diverse polyketides. However, the interaction specificity between ATs and unusual acyl units is rarely documented. In Streptomycestsukubaensis YN06, we found that AT4<sub>FkbB</sub> [an AT in the fourth module of tacrolimus (FK506) PKS] transferred both allylmalonyl (allmal) and emthylmalonyl (ethmal) units to ACPs, which was supposed responsible for the production of both FK506 and its analog FK520, respectively. Mutations of five residues in AT4<sub>FkbB</sub> (Q119A, L185I-V186D-V187T, and F203L) caused decreased efficiency of allmal transfer, but a higher ratio of ethmal transfer, supposedly due to less nucleophilic attacks between Ser599 in the active site of AT4<sub>FkbB</sub> and the carbonyl carbon in the allmal unit, as observed from molecular dynamics simulations. Furthermore, reverse mutations of these five residues in ethmal-specific ATs to the corresponding residues of AT4<sub>FkbB</sub> increased its binding affinity to allmal-CoA. Among these residues, Val187 of AT4<sub>FkbB</sub> mainly contributed to allmal recognition, and V187K mutant produced less FK520 than wild type. Our findings thus suggested that five critical residues within AT4<sub>FkbB</sub> were important for AT functionality in polyketide extension and potentially for targeting biosynthesis by generating desirable products and eliminating undesirable analogs.</p
Identification and Biosynthetic Characterization of Natural Aromatic Azoxy Products from <i>Streptomyces chattanoogensis</i> L10
Aromatic azoxy compounds
recently attracted wide interest for their
unique liquid crystalline properties. However, biosynthetic pathways
of natural azoxy products have rarely been reported. Three novel aromatic
azoxy compounds, azoxymycins A, B, and C, have been isolated and identified
from <i>Streptomyces chattanoogensis</i> L10, and their
biosynthetic pathways have been reported
Efficient Biosynthesis of Fungal Polyketides Containing the Dioxabicyclo-octane Ring System
Aurovertins are fungal polyketides
that exhibit potent inhibition
of adenosine triphosphate synthase. Aurovertins contain a 2,6-dioxabicyclo[3.2.1]octane
ring that is proposed to be derived from a polyene precursor through
regioselective oxidations and epoxide openings. In this study,
we identified only four enzymes required to produce aurovertin
E. The core polyketide synthase produces a polyene α-pyrone.
Following pyrone <i>O-</i>methylation by a methyltransferase,
a flavin-dependent mono-oxygenase and an epoxide hydrolase can iteratively
transform the terminal triene portion of the precursor into the dioxabicyclo[3.2.1]octane
scaffold. We demonstrate that a tetrahydrofuranyl polyene
is the first stable intermediate in the transformation, which can
undergo epoxidation and anti-Baldwin 6-<i>endo</i>-tet ring
opening to yield the cyclic ether product. Our results further demonstrate
the highly concise and efficient ways in which fungal biosynthetic
pathways can generate complex natural product scaffolds