Orthogonal AARS Variants via Phage-Assisted Continuous Evolution
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Solution Overview
Problem
Traditional laboratory evolution techniques for aminoacyl-tRNA synthetases (AARSs) result in enzymes with significantly reduced activity and poor amino acid selectivity, limiting their utility in genetic code expansion and protein production with non-canonical amino acids.
Innovation Solution
The use of phage-assisted continuous evolution (PACE) methods for evolving orthogonal AARSs, which enables rapid and continuous improvement of enzymatic efficiency and selectivity by employing positive and negative selection strategies over multiple generations, resulting in highly active and selective AARS variants such as pyrrolysyl-tRNA synthetase (PylRS) and tyrosyl-tRNA synthetase (TyrRS) variants.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional laboratory evolution techniques are used to evolve AARSs with altered amino acid specificity, then amino acid selectivity is improved, but enzymatic activity is reduced by approximately 1,000-fold
Solution Approach 1:
The patent implements continuous evolution through PACE methodology, where phage-encoded AARS variants are continuously propagated and selected over hundreds of generations in a chemostat system. This continuous evolutionary pressure maintains high enzymatic activity while progressively improving amino acid selectivity, resolving the contradiction between activity and selectivity that plagues traditional batch evolution methods.
Solution Approach 2:
The system incorporates dual positive and negative selection feedback mechanisms. Positive selection enriches variants with desired ncAA incorporation activity, while negative selection simultaneously eliminates variants with unwanted canonical amino acid activity. This feedback loop enables the evolution of high selectivity without sacrificing activity, as both properties are monitored and selected for concurrently.
2Loss of time
If few rounds of selection are conducted to reduce evolution time, then time is saved, but AARS variants emerge with suboptimal activity and selectivity
Solution Approach 1:
PACE enables continuous evolution over hundreds of generations in a single extended experiment, equivalent to many sequential batch experiments running simultaneously. The chemostat system maintains continuous flow and selection pressure, allowing rapid accumulation of beneficial mutations while maintaining constant evolutionary pressure, thereby achieving high reliability without proportionally increasing time investment.
Solution Approach 2:
The system pre-establishes a library of diverse AARS variants with randomized residues in the amino acid-binding pocket before initiating evolution. This preliminary diversification ensures that beneficial mutations are present in the population from the start, allowing rapid selection and enrichment of high-performance variants without requiring extensive de novo mutation screening during the evolution process.
3Quantity of substance
If high concentrations of ncAA are used to compensate for low selectivity, then amino acid incorporation is maintained, but protein yields are lowered due to minimal media requirements
Solution Approach 1:
Negative selection in the PACE system applies feedback pressure to eliminate AARS variants that incorporate canonical amino acids incorrectly. By continuously selecting against unwanted amino acid incorporation, the system evolves variants with high selectivity that function effectively at physiological ncAA concentrations, eliminating the need for compensatory high ncAA additions that would otherwise be required and thereby maintaining high protein yields.
Data Source
AI summary
The disclosure provides amino acid sequence variants of orthogonal aminoacyl-tRNA synthetases (AARSs) having increased activity and selectivity compared to previous AARSs, and methods of producing the same.