Engineered E. coli Host for Toxic Gene Expression
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Solution Overview
Problem
Current inducible cell systems for expressing toxic proteins face challenges such as basal expression of toxic proteins, lag time in protein production after induction, high costs due to antibiotic requirements, interference with target protein expression, cell lysis, and reduced yield, particularly when using multi-copy plasmids like pLysE for extremely toxic genes.
Innovation Solution
A genetically engineered E. coli host cell with a single copy of T7 RNA polymerase genes and a T7 RNA polymerase inhibitor, such as mutant T7 lysozyme, is developed, where the T7 lysozyme is expressed from a constitutive promoter, and LacIq is optionally included to control basal T7 RNA polymerase activity, allowing for reduced basal expression and improved protein yield without the need for antibiotics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multi-copy plasmids (pLysE, pLysS) are used to express T7 lysozyme, then basal T7 RNA polymerase activity is reduced, but lag time after induction increases and protein yield decreases
Solution Approach 1:
The patent changes the copy number parameter from multi-copy (pLysE, pLysS) to single-copy (F′ plasmid), and modifies the T7 lysozyme protein sequence (mutations Y46F, K128Q, K128Y, K128M, K128W, K128I) to alter its inhibitory activity. This allows achieving effective basal expression control with lower lysozyme levels, reducing the lag time after induction while maintaining productivity.
2Reliability
If multi-copy plasmids are used to maintain T7 lysozyme, then basal expression control is improved, but antibiotic requirements increase cost
Solution Approach 1:
The patent changes the plasmid copy number from multi-copy to single-copy (F′ plasmid), which stabilizes the system and allows elimination of antibiotic selection pressure. The modified T7 lysozyme variants provide sufficient inhibitory activity at single-copy levels, enabling cost-effective production without continuous antibiotic addition.
3Reliability
If T7 lysozyme is constitutively expressed, then basal T7 RNA polymerase activity is inhibited, but cell lysis increases and viability decreases
Solution Approach 1:
The patent introduces specific mutations in the T7 lysozyme sequence (Y46F, K128Q, K128Y, K128M, K128W, K128I) that modify its activity profile. These variants provide sufficient T7 RNA polymerase inhibition at lower expression levels, preventing the excessive cell lysis associated with wild-type lysozyme while maintaining reliable basal expression control.
4Reliability
If wild-type T7 lysozyme is expressed at high levels, then T7 RNA polymerase activity is strongly inhibited, but protein translation burden increases and target protein yield decreases
Solution Approach 1:
The patent modifies the T7 lysozyme protein sequence to create variants (Y46F, K128Q, K128Y, K128M, K128W, K128I) that achieve effective T7 RNA polymerase inhibition at lower expression levels. This reduces the translational burden on the cell, allowing more resources to be allocated to target protein synthesis and increasing overall productivity.
Data Source
AI summary
Compositions and methods are provided for expression of a toxic protein in a host cell preferably a bacterial host cell where at least one T7 RNA polymerase gene Is contained on the host cell chromosome and one or more genes encoding a T7 RNA polymerase inhibitor is located on an F′ plasmid or on the chromosome.