Biochemistry‐Guided Prediction of the Absolute Configuration of Fungal Reduced Polyketides

Abstract

Highly reducing polyketide synthases (HR-PKSs) produce structurally diverse polyketides (PKs). The PK diversity is constructed by av ariety of factors,i ncluding the b-keto processing,c hain length, methylation pattern, and relative and absolute configurations of the substituents.W e examined the stereochemical course of the PK processing for the synthesis of polyhydroxyPKs such as phialotides,phomenoic acid, and ACR-toxin. Heterologous expression of aH R-PKS gene,atrans-acting enoylreductase gene,and atruncated non-ribosomal peptide synthetase gene resulted in the formation of al inear PK with multiple stereogenic centers.T he absolute configurations of the stereogenic centers were determined by chemical degradation followed by comparison of the degradation products with synthetic standards.As tereochemical rule was proposed to explain the absolute configurations of other reduced PKs and highlights an error in the absolute configurations of ar eported structure.T he present work demonstrates that focused functional analysis of functionally related HR-PKSs leads to ab etter understanding of the stereochemical course.

Identification of PKS-NRPS Hybrid Metabolites in Marine-Derived Penicillium oxalicum

“…The OpdC served as trans -acting ER and reduced the terminal alkenyl to alkane. According to the stereochemical rule proposed by Oikawa and coworkers [ 16 ], the absolute configurations in C15 and C17 were formed at the chain extension stages in the PKS-NRPS assembly line ( Figure S31 ). The differences between 15 S , 17 R in 1 and 15 R , 17 S in 2 were generated by non-stereospecific catalysis of the ketoreductase (KR) domain and enoyl reductases.…”

Mono-/Bis-Alkenoic Acid Derivatives From an Endophytic Fungus Scopulariopsis candelabrum and Their Antifungal Activity

“…For the stereochemistry of reported mono-/bis-alkenoic acid derivatives, the configurations of C-7 (7′) and C-13 (13′) were conserved to be 7 R (7′ R ) and 13 S (13′ S ) ( Liu et al, 2018 ; Niu et al, 2019 ; Tang et al, 2019 ), while the configuration of C-12 (12′) turned out to be 12 (12′) R or 12 (12′) S ( Liu et al, 2018 ). Recently, it was reported that the configurations of fungal polyketides were conserved in general with few exceptions ( Takino et al, 2021 ). Therefore, in view of the shared biosynthetic pathway of mono-/bis-alkenoic acid derivatives, as well as previous literature reports ( Liu et al, 2018 ; Niu et al, 2019 ; Tang et al, 2019 ), the configurations of C-7 (7′) and C-13 (13′) in 2 were supposed to be 7 R (7′ R ) and 13 S (13′ S ), respectively.…”

Studying a Bottleneck of Multimodular Polyketide Synthase Processing: the Polyketide Structure-Dependent Performance of Ketoreductase Domains

“…The conversion of multiple PKS intermediates by one KR domain is reminiscent of HR-PKS, for which a common stereochemical explanation for substrate-dependent stereoselectivity was recently devised. 31 MycKRB is a general B-type KR that acts as B0-or B1-type depending on the biosynthetic precursor. 19,27 The KR domains were produced as N-terminal His 6 -tagged fusion proteins by heterologous expression in Escherichia coli and purified (Figure S1).…”

“…Detailed studies with a larger number of KRs and substrate surrogates that cover a broader structural range are clearly necessary as well as the linking of in vitro results to KR and PKS module structural data. Particularly the outcome of KR reactions with polyketides of backbone lengths > C 6 could provide new insights, as such have only been applied in a few in vitro studies with KR domains from HR-PKS 30,31 and multimodular type I PKS. 27,35 It will also be important to reassess the observed performance of KR domains in the whole PKS module environment.…”

“…EryKR1 (B2-type) and TylKR1 (B1-type) are domains from the first modules of macrolactone-forming PKS with an expectable preference for short-chain substrate surrogates. ,,,− AmpKR2 (A1-type) from the third module of the amphotericin PKS should prefer longer chains than EryKR1 and TylKR1. ,, EryKR6 (A1-type) from the terminal module of the erythronolide B-forming PKS naturally converts a polar heptaketide, so that a strong preference for long-chain substrates can be expected. ,, MycKRA (A0-type) and MycKRB (B-type) each occur in multiple modules of the mycolactone-forming PKS. , Their natural substrates span a wide structural range, from diketide 46 to hexaketide 48 or decaketide 51 , respectively. The conversion of multiple PKS intermediates by one KR domain is reminiscent of HR-PKS, for which a common stereochemical explanation for substrate-dependent stereoselectivity was recently devised . MycKRB is a general B-type KR that acts as B0- or B1-type depending on the biosynthetic precursor. , …”