Optogenetic Gene Expression Control in Yeast Fermentation
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Solution Overview
Problem
Current inducible systems in metabolic engineering for controlling gene expression in yeast are limited by the use of chemical inducers and repressors, which are coarse, persistent, and difficult to tune, and do not allow for precise control over enzyme expression levels, especially when dealing with toxic products or competing metabolic pathways.
Innovation Solution
A light-controlled gene expression system using the OptoEXP and OptoINVRT systems, based on the EL222 light-sensitive transcription factor, which enables bidirectional control of gene expression in yeast, allowing for precise tuning of metabolic pathways and separation of growth and production phases using varying light doses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If chemical inducers or repressors are used to control gene expression, then gene expression can be regulated, but the control is coarse and persistent, making it difficult to tune and practically impossible to reverse
Solution Approach 1:
The patent replaces chemical induction systems with an optogenetic system using the EL222 transcription factor that responds to light of specific wavelengths. This substitution allows precise, reversible, and tunable control of gene expression through light dosing, overcoming the limitations of chemical inducers which are coarse and persistent. The light-controlled system enables dynamic adjustment of enzyme expression levels during fermentation.
Solution Approach 2:
The patent utilizes the ability to change light parameters (wavelength, intensity, duration) to precisely control the expression levels of genes in the metabolic pathway. By varying light dosing parameters, the system can tune enzyme expression to optimal levels for different fermentation phases, providing continuous adjustability that chemical systems cannot achieve.
2Productivity
If inducible systems are used to separate cell growth from product formation, then metabolic burden is reduced, but the systems place restrictions on media composition
Solution Approach 1:
The patent replaces chemical-inducible systems with light-controlled optogenetic systems. This substitution removes restrictions on media composition because light does not interfere with nutrient availability or metabolic pathways. The EL222 transcription factor can be controlled by light regardless of the carbon source or other media components, providing full flexibility in media design for optimal productivity.
3Reliability
If chemical inducers are used for gene expression control, then gene expression can be regulated, but the effects are difficult to tune and practically impossible to reverse
Solution Approach 1:
The patent substitutes chemical inducers with light as the control signal. Light provides immediate and reversible control of the EL222 transcription factor, allowing gene expression to be turned on or off dynamically during fermentation. This reversibility enables the system to adapt expression levels in real-time based on fermentation progress, unlike chemical systems where effects are persistent and difficult to reverse.
Solution Approach 2:
The patent employs periodic light dosing to control gene expression throughout the fermentation process. By applying light in specific patterns and durations, the system can dynamically regulate enzyme expression levels to match the changing metabolic needs of the fermentation, providing temporal control that chemical systems cannot achieve.
4Measurement precision
If light-controlled gene expression is implemented, then precise tuning of metabolic pathways is achieved, but system complexity increases
Solution Approach 1:
The patent uses the EL222 transcription factor as an intermediary between light input and gene expression output. This intermediary component translates light signals into controlled transcriptional activity, providing a biological interface that simplifies the overall control architecture. The EL222 system integrates multiple light-response functions into a single molecular mediator, reducing the need for complex external control mechanisms.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This system enables robust growth on glucose while producing valuable chemicals like lactate or isobutanol by controlling gene expression with light, achieving high yields and optimizing chemical production by varying light schedules during fermentation.
Implementation Method 1
a first sequence comprising a nucleotide sequence that encodes a light-activated transcription factor that binds to promoter sequences and initiates transcription under certain wavelengths of light
Data Source
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AI summary
A system and method for controlling metabolic enzymes or pathways in cells to produce a chemical above the levels of a wild-type strain is disclosed. The system utilizes cells, including yeasts, bacteria, and molds, having at least two genes capable of being controlled bi-directionally with light, where one gene is turned from off to on when exposed to light and another gene is turned from on to off when exposed to light, the two genes reversing when the light is turned off. Cells may utilize any number of sequences that benefit chemical production, including sequences that: encode for constitutive transcription of light-activated transcription factor fusions; encode for a metabolic enzyme; encode for a repressor; induce expression of metabolic enzymes; and an endogenous or exogenous activator expressed by a constitutive promoter, inducible promoter, or gene circuit.