KpnI Restriction Endonuclease Mutants for Star Activity Reduction
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Solution Overview
Problem
KpnI restriction endonuclease exhibits significant star activity in standard buffers, leading to non-specific cleavage of DNA substrates, particularly at high enzyme concentrations and in longer DNA pieces, which complicates precise genetic manipulation.
Innovation Solution
Modification of the KpnI restriction endonuclease by introducing specific mutations in the PDX...D/EXK catalytic motif, such as D163I or K165A, and using a calcium ion-based buffer to reduce star activity, while maintaining effective cleavage efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If KpnI restriction endonuclease is used at high enzyme concentrations, then DNA cleavage efficiency is improved, but star activity (non-specific cleavage) increases
Solution Approach 1:
The patent applies parameter changes by modifying the enzyme's amino acid sequence (creating mutants with substitutions at positions 163 and/or 165) and changing the buffer composition (using calcium ions instead of magnesium ions). These parameter modifications reduce star activity while preserving specific DNA cleavage activity, allowing high enzyme concentrations to be used without excessive non-specific cleavage.
2Reliability
If standard buffer conditions are used, then enzyme activity is maintained, but non-specific cleavage occurs
Solution Approach 1:
The patent changes the buffer parameter from standard magnesium-based buffer to a calcium-based buffer system. This parameter change selectively reduces non-specific cleavage (star activity) while maintaining specific DNA cleavage activity, thereby improving the reliability of the enzyme for precise genetic manipulation applications.
3Manufacturing precision
If KpnI is used for precise genetic manipulation, then specific cleavage is achieved, but star activity complicates the manipulation
Solution Approach 1:
The patent employs parameter changes through enzyme mutagenesis (substitutions at positions 163 and/or 165 in the catalytic motif) and buffer composition modification (calcium ion substitution). These changes reduce star activity to minimal levels while preserving specific cleavage at the target site, enabling precise genetic manipulation without the complicating effects of non-specific cleavage.
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
The modified KpnI restriction endonuclease demonstrates significantly reduced star activity, ensuring precise DNA cleavage with minimal non-specific cuts, even at high enzyme concentrations and in calcium buffers, thereby enhancing the reliability of genetic manipulation techniques.
Implementation Method 1
KpnI restriction endonuclease binds to DNA in the absence of metal ions and cleaves in the presence of Mg2+
Implementation Method 2
KpnI restriction endonuclease from Klebsiella pneumoniae, was characterized by Tomassini et al.
Implementation Method 3
KpnI restriction endonuclease binds to DNA in the absence of metal ions and cleaves in the presence of Mg2+
Implementation Method 4
having a catalytic motif PDX . . . D/EXK (SEQ ID NO:16) wherein one, or more amino acids in the motif are mutated
Data Source
AI summary
Methods are provided for making restriction endonucleases with reduced star activity by one or more targeted mutations to a catalytic site within the restriction endonuclease. Examples of modifications to restriction endonucleases with significant sequence identity with KpnI are provided and reduced star activity demonstrated.