Structural basis of the complementary activity of two ketosynthases in aryl polyene biosynthesis

Woo Cheol Lee,Ahjin Jang,Jiwon Yeon,Eunha Hwang,Yangmee Kim,Sungjae Choi

doi:10.1038/s41598-021-95890-y

Woo Cheol Lee, Ahjin Jang + Show 4 more

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https://doi.org/10.1038/s41598-021-95890-y

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Abstract

Aryl polyenes (APE) are one of the most widespread secondary metabolites among gram-negative bacteria. In Acinetobacter baumannii, strains belonging to the virulent global clone 2 (GC2) mostly contain APE biosynthesis genes; its relevance in elevated pathogenicity is of great interest. APE biosynthesis gene clusters harbor two ketosynthases (KSs): the heterodimeric KS-chain length factor complex, ApeO-ApeC, and the homodimeric ketoacyl-acyl carrier protein synthase I (FabB)-like KS, ApeR. The role of the two KSs in APE biosynthesis is unclear. We determined the crystal structures of the two KSs from a pathogenic A. baumannii strain. ApeO-ApeC and ApeR have similar cavity volumes; however, ApeR has a narrow cavity near the entrance. In vitro assay based on the absorption characteristics of polyene species indicated the generation of fully elongated polyene with only ApeO-ApeC, probably because of the funnel shaped active site cavity. However, adding ApeR to the reaction increases the throughput of APE biosynthesis. Mutagenesis at Tyr135 in the active site cavity of ApeR reduces the activity significantly, which suggests that the stacking of the aryl group between Tyr135 and Phe202 is important for substrate recognition. Therefore, the two KSs function complementarily in the generation of APE to enhance its production.

Highlights

Aryl polyenes (APE) are one of the most widespread secondary metabolites among gram-negative bacteria
We found that Acinetobacter baumannii, a notorious nosocomial pathogen, contains APE biosynthetic gene cluster (BGC), especially among the global clone 2 (GC2), which have enhanced virulence[10]
The truncated residues formed the first helix in XdApeC and Paraburkholderia phymatum ApeC (PpApeC) (Fig. 2A, arrow)

Summary

Introduction

Aryl polyenes (APE) are one of the most widespread secondary metabolites among gram-negative bacteria. APE biosynthesis gene clusters harbor two ketosynthases (KSs): the heterodimeric KS-chain length factor complex, ApeO-ApeC, and the homodimeric ketoacyl-acyl carrier protein synthase I (FabB)-like KS, ApeR. The mechanism of HR-PKS is more similar to that of FAS; the final step of ER is skipped often to generate compounds with conjugated double bonds. These polyene polyketides, produced by various actinomycetes and fungi, display diverse b ioactivities[7]. There is a large family of biosynthetic gene cluster (BGC) coding for aryl polyene (APE) biosynthesis genes[8] These BGCs are common in gram-negative bacteria and the enzymes catalyze the synthesis of 4-hydroxybenzoyl (4HB) polyene compounds with 6 to 7 double bonds. We found that Acinetobacter baumannii, a notorious nosocomial pathogen, contains APE BGC, especially among the global clone 2 (GC2), which have enhanced virulence[10]

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