Activation, Structure, Biosynthesis and Bioactivity of Glidobactin-like Proteasome Inhibitors from Photorhabdus laumondii.

Lei Zhao,Michael Groll,Marcel Kaiser,Helge B Bode,Alexander O Brachmann,Camille Le Chapelain

doi:10.1002/cbic.202100014

Abstract

The glidobactin‐like natural products (GLNPs) glidobactin A and cepafungin I have been reported to be potent proteasome inhibitors and are regarded as promising candidates for anticancer drug development. Their biosynthetic gene cluster (BGC) plu1881–1877 is present in entomopathogenic Photorhabdus laumondii but silent under standard laboratory conditions. Here we show the largest subset of GLNPs, which are produced and identified after activation of the silent BGC in the native host and following heterologous expression of the BGC in Escherichia coli. Their chemical diversity results from a relaxed substrate specificity and flexible product release in the assembly line of GLNPs. Crystal structure analysis of the yeast proteasome in complex with new GLNPs suggests that the degree of unsaturation and the length of the aliphatic tail are critical for their bioactivity. The results in this study provide the basis to engineer the BGC for the generation of new GLNPs and to optimize these natural products resulting in potential drugs for cancer therapy.

Highlights

The ubiquitin-proteasome system (UPS) is the main nonlysosomal protein degradation system responsible for the degradation of damaged, misfolded and excess proteins in all eukaryotic cells.[1,2] It plays a crucial role in the dynamic regulation of protein turnover, which is essential for cell cycle, apoptosis, regulation of gene expression and other cellular functions.[3,4][b] Dr L
Their biosynthetic gene cluster (BGC) was first identified from the soil bacterium Burkholderia K481-B101.[24]. The BGC is composed of eight genes, named glbA-H (Figure 1b), in which glbF and glbC encode a non-ribosomal peptide synthetase (NRPS) and a hybrid NRPS-polyketide synthetase (PKS), respectively, for the biosynthesis of the tripeptide part in Glidobactin-like natural products (GLNPs) (Figure 1c).[24]
Bioinformatic analysis showed that the homologous BGC, consisting of five genes plu1881–1877, is present in entomopathogenic Photorhabdus laumondii but lacking glbA, In previous study, a heterologous expression of the plu1881– 1877 in Pseudomonas putida, which can bypass endogenous regulatory control, was found capable of producing 1.[25] our effort of cloning the complete BGC into Escherichia coli resulted in successful production of 1 and its derivatives (Figure S1 in the Supporting Information)

Summary

Introduction

The ubiquitin-proteasome system (UPS) is the main nonlysosomal protein degradation system responsible for the degradation of damaged, misfolded and excess proteins in all eukaryotic cells.[1,2] It plays a crucial role in the dynamic regulation of protein turnover, which is essential for cell cycle, apoptosis, regulation of gene expression and other cellular functions.[3,4]. Glidobactin-like natural products (GLNPs) such as glidobactins, cepafungins and luminmycins consist of similar structural scaffolds (Figure 1a).[16,17] Luminmycins are the 10-deoxy derivatives of glidobactins,[18] while cepafungins only differ in the aliphatic tails.[19] GLNPs characterize a common 12-membered macrolactam ring with an α,β-unsaturated carbonyl group. Bioactivity testing revealed their strong cytotoxicity against various human cancer cells.[20,21] The mechanism behind the activity is the potent inhibition of proteasome.[22] Crystal. One explanation might be that the expression of the BGC is strictly regulated and solely induced by the specific environmental condition, in view of the unique niche of P. laumondii in the nematodesymbiotic and insect-pathogenic relationships.[21,26] we report the activation, structure, biosynthesis and bioactivity of GLNP proteasome inhibitors from P. laumondii

Results and Discussion

Conclusion

Conflict of Interest