A squalene synthase protein degradation method for improved sesquiterpene production in Saccharomyces cerevisiae

Peng, Bingyin, Plan, Manuel R., Chrysanthopoulos, Panagiotis, Hodson, Mark P., Nielsen, Lars K. and Vickers, Claudia E. (2017) A squalene synthase protein degradation method for improved sesquiterpene production in Saccharomyces cerevisiae. Metabolic Engineering, 39 209-219. doi:10.1016/j.ymben.2016.12.003

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Author Peng, Bingyin
Plan, Manuel R.
Chrysanthopoulos, Panagiotis
Hodson, Mark P.
Nielsen, Lars K.
Vickers, Claudia E.
Title A squalene synthase protein degradation method for improved sesquiterpene production in Saccharomyces cerevisiae
Formatted title
A squalene synthase protein degradation method for improved sesquiterpene production in Saccharomyces cerevisiae
Journal name Metabolic Engineering   Check publisher's open access policy
ISSN 1096-7184
1096-7176
Publication date 2017-01-01
Year available 2016
Sub-type Article (original research)
DOI 10.1016/j.ymben.2016.12.003
Open Access Status File (Author Post-print)
Volume 39
Start page 209
End page 219
Total pages 11
Place of publication Waltham, MA, United States
Publisher Academic Press
Language eng
Subject 1305 Biotechnology
1502 Bioengineering
2402 Applied Microbiology and Biotechnology
Abstract Sesquiterpenes are C15 isoprenoids with utility as fragrances, flavours, pharmaceuticals, and potential biofuels. Microbial fermentation is being examined as a competitive approach for bulk production of these compounds. Competition for carbon allocation between synthesis of endogenous sterols and production of the introduced sesquiterpene limits yields. Achieving balance between endogenous sterols and heterologous sesquiterpenes is therefore required to achieve economical yields. In the current study, the yeast Saccharomyces cerevisiae was used to produce the acyclic sesquiterpene alcohol, trans-nerolidol. Nerolidol production was first improved by enhancing the upstream mevalonate pathway for the synthesis of the precursor farnesyl pyrophosphate (FPP). However, excess FPP was partially directed towards squalene by squalene synthase (Erg9p), resulting in squalene accumulation to 1% biomass; moreover, the specific growth rate declined. In order to re-direct carbon away from sterol production and towards the desired heterologous sesquiterpene, a novel protein destabilisation approach was developed for Erg9p. It was shown that Erg9p is located on endoplasmic reticulum and lipid droplets through a C-terminal ER-targeted transmembrane peptide. A PEST (rich in Pro, Glu/Asp, Ser, and Thr) sequence-dependent endoplasmic reticulum-associated protein degradation (ERAD) mechanism was established to decrease cellular levels of Erg9p without relying on inducers, repressors or specific repressing conditions. This improved nerolidol titre by 86% to ~100 mg L. In this strain, squalene levels were similar to the wild-type control strain, and downstream ergosterol levels were slightly decreased relative to the control, indicating redirection of carbon away from sterols and towards sesquiterpene production. There was no negative effect on cell growth under these conditions. Protein degradation is an efficient mechanism to control carbon allocation at flux-competing nodes in metabolic engineering applications. This study demonstrates that an engineered ERAD mechanism can be used to balance flux competition between the endogenous sterol pathway and an introduced bio-product pathways at the FPP node. The approach of protein degradation in general might be more widely applied to improve metabolic engineering outcomes.
Formatted abstract
Sesquiterpenes are C15 isoprenoids with utility as fragrances, flavours, pharmaceuticals, and potential biofuels. Microbial fermentation is being examined as a competitive approach for bulk production of these compounds. Competition for carbon allocation between synthesis of endogenous sterols and production of the introduced sesquiterpene limits yields. Achieving balance between endogenous sterols and heterologous sesquiterpenes is therefore required to achieve economical yields. In the current study, the yeast Saccharomyces cerevisiae was used to produce the acyclic sesquiterpene alcohol, trans-nerolidol. Nerolidol production was first improved by enhancing the upstream mevalonate pathway for the synthesis of the precursor farnesyl pyrophosphate (FPP). However, excess FPP was partially directed towards squalene by squalene synthase (Erg9p), resulting in squalene accumulation to 1% biomass; moreover, the specific growth rate declined. In order to re-direct carbon away from sterol production and towards the desired heterologous sesquiterpene, a novel protein destabilisation approach was developed for Erg9p. It was shown that Erg9p is located on endoplasmic reticulum and lipid droplets through a C-terminal ER-targeted transmembrane peptide. A PEST (rich in Pro, Glu/Asp, Ser, and Thr) sequence-dependent endoplasmic reticulum-associated protein degradation (ERAD) mechanism was established to decrease cellular levels of Erg9p without relying on inducers, repressors or specific repressing conditions. This improved nerolidol titre by 86% to ~100 mg L−1. In this strain, squalene levels were similar to the wild-type control strain, and downstream ergosterol levels were slightly decreased relative to the control, indicating redirection of carbon away from sterols and towards sesquiterpene production. There was no negative effect on cell growth under these conditions. Protein degradation is an efficient mechanism to control carbon allocation at flux-competing nodes in metabolic engineering applications. This study demonstrates that an engineered ERAD mechanism can be used to balance flux competition between the endogenous sterol pathway and an introduced bio-product pathways at the FPP node. The approach of protein degradation in general might be more widely applied to improve metabolic engineering outcomes.
Keyword Endoplasmic reticulum-associated protein degradation (ERAD)
Metabolic engineering
Saccharomyces cerevisiae
Sesquiterpene
Trans-nerolidol
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: HERDC Pre-Audit
Australian Institute for Bioengineering and Nanotechnology Publications
 
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