AAV Capsid Gene Codon Optimization for VP1/VP2/VP3 Stoichiometry
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Solution Overview
Problem
The challenge in producing recombinant adeno-associated virus (AAV) vectors lies in achieving efficient and proportional expression of capsid proteins VP1, VP2, and VP3, particularly in insect cells, due to inefficient promoter sequences and random assembly ratios, which complicates scaling up production.
Innovation Solution
A method involving codon optimization and the use of different start codons for VP1, VP2, and VP3, along with specific codon mutations to reduce initial translation strength, is employed to optimize the expression of capsid proteins, using a weak start codon for VP1 and VP2 and a strong start codon for VP3, and optimizing additional coding segments to achieve a 1:1:10 stoichiometric ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single cap gene is used to encode VP1, VP2, and VP3 through different start codons in insect cells, then the production process is simplified and scalability is improved, but the expression efficiency and proportional stoichiometry of the three capsid proteins deteriorate due to inefficient promoter sequences in insect cells
Solution Approach 1:
The patent applies local quality by differentiating the start codons for each capsid protein (VP1, VP2, VP3) within the single cap gene. Each protein is assigned a specific start codon (ATG, GTG, TTG) with different translation efficiencies, creating localized expression control points that optimize the stoichiometric ratio of capsid proteins in insect cells while maintaining the simplicity of a single gene structure
Solution Approach 2:
The patent changes the parameter of start codon selection to optimize protein expression. By selecting start codons with varying translation initiation strengths (ATG being strongest, followed by GTG, then TTG), the patent adjusts the relative expression levels of VP1, VP2, and VP3 to achieve the desired 1:1:10 stoichiometric ratio, thereby resolving the expression efficiency problem in insect cells
2Speed
If random assembly of VP1, VP2, and VP3 is allowed, then the assembly process is simple and fast, but the stoichiometric ratio control deteriorates, making it difficult to achieve the desired 1:1:10 ratio
Solution Approach 1:
The patent applies preliminary action by pre-establishing the correct stoichiometric ratio of VP1:VP2:VP3 through optimized start codon selection before the assembly process begins. This ensures that when assembly occurs, the proteins are already in the correct proportions (1:1:10), eliminating the need for complex post-assembly ratio adjustments while maintaining simple and fast assembly kinetics
3Reliability
If mammalian cell transient transfection is used for AAV packaging, then the capsid structure is similar to wild type, but the culture requirements (adherent culture, serum addition) create difficulties in scaling up production
Solution Approach 1:
The patent applies mechanics substitution by replacing the complex mammalian cell culture system (requiring adherent culture and serum addition) with an insect cell expression system. This substitution maintains capsid structure fidelity through proper VP protein stoichiometry while dramatically improving scalability, as insect cell suspension culture does not require serum or special adherent conditions
4Object-affected harmful factors
If the injection dose is reduced to ensure better safety, then the therapeutic safety is improved, but the production cost and high-titer pressure increase
Solution Approach 1:
The patent applies parameter changes by optimizing the start codon selection to achieve high-level expression of all three capsid proteins (VP1, VP2, VP3) in the correct stoichiometric ratio. This increases the overall titer of functional AAV particles produced, thereby reducing the injection dose required for therapy while simultaneously lowering production costs through more efficient manufacturing
Data Source
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AI summary
Provided are a method for modifying a capsid protein coding sequence of a cap gene of an adeno-associated virus (AAV), and an AAV capsid protein coding sequence obtained via the method. Additionally provided is the use of a modified AAV capsid protein coding sequence for expressing recombinant AAV and proteins of interest.