Membrane Protein Expression Vector Using P9 Fusion Partner
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Solution Overview
Problem
Current methods for expressing membrane proteins, especially multipass transmembrane proteins, are inefficient due to host cell death and low expression yields, making it difficult to produce these economically important proteins using recombinant DNA techniques.
Innovation Solution
An expression vector utilizing the major envelope protein P9 of Cystovirus phi6 as a fusion partner, combined with a multicloning site and a protease recognition site, is used to effectively express target membrane proteins by transforming cells and culturing them, allowing for higher yields and proper membrane integration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If membrane proteins are expressed using conventional recombinant DNA techniques in E. coli, then protein expression is attempted, but host cell death occurs before observable protein expression
Solution Approach 1:
The patent uses a fusion protein strategy where the target membrane protein is fused with a soluble protein partner (such as maltose binding protein, glutathion S-transferase, or thioredoxin) to create an intermediary complex. This fusion protein can be expressed in E. coli without causing cell death, as the soluble partner mitigates the toxic effects of the membrane protein. The fusion protein can then be purified and the membrane protein released through proteolytic cleavage, thus resolving the contradiction between achieving high protein expression and maintaining host cell viability.
Solution Approach 2:
The patent segments the membrane protein expression system into separate functional components: a soluble expression vector containing the membrane protein gene fused with a soluble partner protein, and a separate protease system for cleavage. This segmentation allows the membrane protein to be expressed in a controlled manner without directly impacting host cell viability, as the toxic membrane protein is sequestered in the soluble fusion complex until needed for purification.
2Productivity
If membrane proteins are expressed using conventional methods, then expression is attempted, but expression yield is extremely low
Solution Approach 1:
The soluble protein partner acts as an intermediary that facilitates high-level expression of the membrane protein. The fusion protein complex can be expressed at high levels in E. coli because the soluble partner does not cause cell death, thereby enabling high productivity. The partner protein also serves as a purification tag, making the membrane protein easier to isolate and purify, thus improving both yield and ease of manufacture.
Solution Approach 2:
The soluble protein partner performs multiple functions simultaneously: it acts as a fusion partner to enable high-level expression, serves as a purification tag for easy isolation, and can be used to determine protein folding and structure. This multi-functionality resolves the contradiction by improving both expression yield and ease of manufacture through a single strategic choice of partner protein.
3Productivity
If fusion proteins are used to express membrane proteins in E. coli, then expression is attempted, but the amount of expressed protein is very small
Solution Approach 1:
The patent changes the parameters of the expression system by selecting specific soluble protein partners with optimized properties. Partners such as maltose binding protein, glutathion S-transferase, and thioredoxin were chosen based on their ability to form stable fusion complexes, their ease of purification, and their compatibility with E. coli expression systems. This optimization of parameters enables significantly higher expression amounts compared to conventional methods.
Solution Approach 2:
The soluble protein partner serves as an intermediary that bridges the gap between the membrane protein and the E. coli expression system. The fusion complex allows the membrane protein to be expressed at high levels without causing cell death, and the partner protein facilitates efficient purification, thereby increasing the quantity of expressed membrane protein from trace amounts to measurable yields.
Data Source
AI summary
The present invention relates to a membrane protein expression vector containing the major envelope protein P9 of Cystovirus phi6 as a fusion partner, to cells transformed by the expression vector, and to a process for producing membrane proteins using the cells. Target proteins can be effectively expressed by the expression vector of the present invention.