AGT Mutants for Protein Labeling via Amino Acid Substitutions
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Solution Overview
Problem
Current methods for detecting and manipulating proteins of interest using AGT fusion proteins are limited by the properties of wild type human O6-alkylguanine-DNA alkyltransferase (hAGT), such as restricted nuclear localization, reduced expression yield, and instability under various conditions, which hinder efficient labeling and detection.
Innovation Solution
Development of AGT mutants with specific amino acid substitutions and deletions that enhance properties like reduced DNA interaction, improved stability, and increased reactivity against O6-alkylguanine substrates, allowing for improved expression, localization, and solubility, and enabling more efficient labeling and detection of proteins of interest.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If wild type hAGT is used for protein detection and manipulation, then the method is simple and straightforward, but the expression yield is reduced and the protein shows restricted nuclear localization
Solution Approach 1:
The patent applies parameter changes by introducing specific amino acid substitutions (Gly160Trp, Asn157Gly, Ser159Glu) into the hAGT protein sequence. These parameter changes in the protein structure fundamentally alter its properties: increasing expression yield, enabling cytoplasmic localization beyond nuclear restriction, and enhancing reactivity toward O6-alkylguanine substrates. This resolves the contradiction by transforming the protein's inherent limitations into improved functional characteristics.
2Reliability
If wild type hAGT is used, then the protein structure is stable and well-defined, but the stability under oxidizing conditions and overall protein stability is reduced
Solution Approach 1:
The patent introduces specific amino acid substitutions (particularly Cys150Ser and Cys150Ala) that change the chemical parameters of the protein. These substitutions replace cysteine residues prone to oxidation with serine or alanine, fundamentally altering the protein's resistance to oxidizing conditions. This resolves the contradiction by modifying the protein's compositional stability parameters while maintaining its functional integrity.
3Productivity
If wild type hAGT is used for substrate reaction, then the reaction proceeds with natural substrate affinity, but the reactivity against O6-alkylguanine substrates is reduced
Solution Approach 1:
The patent applies parameter changes through mutations at positions 157, 159, and 160 (Asn157Gly, Ser159Glu, Gly160Trp) that directly enhance the protein's reactivity toward O6-alkylguanine substrates. These changes increase the rate of alkyl group transfer while maintaining selectivity for the intended substrates. The parameter changes optimize the reaction kinetics without compromising substrate specificity, resolving the contradiction between enhanced reactivity and maintained specificity.
4Productivity
If wild type hAGT is used, then the protein maintains natural DNA interaction properties, but the DNA binding causes interference with labeling efficiency
Solution Approach 1:
The patent introduces amino acid substitutions (Lys125Ala, Ala127Thr, Arg128Ala) that change the DNA-binding parameters of hAGT. These mutations reduce the protein's affinity for DNA, fundamentally altering its interaction properties. By weakening DNA binding, the mutant proteins prevent DNA from interfering with the labeling process, thereby resolving the contradiction between maintaining natural DNA interaction and achieving efficient labeling.
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 AGT mutants exhibit enhanced stability, expression yield, and reactivity, facilitating effective labeling and detection of proteins, particularly in eukaryotic cells and under oxidizing conditions, thereby improving the efficiency of protein manipulation and analysis.
Implementation Method 1
The underlying mechanism is a nucleophilic reaction of the SN2 type which explains why not only methyl groups, but also benzylic groups are easily transferred.
Data Source
AI summary
The invention relates to AGT mutants showing, when compared to the wild type human AGT, two or more advantageous properties selected from (a) reduced DNA interaction; (b) localisation of the expressed protein in eukaryotic cells that is no longer restricted to the nucleus; (c) improved expression yield as soluble protein and improved stability in various hosts; (d) improved stability under oxidising conditions; (e) improved stability within cells after reaction with a substrate; (f) improved stability outside cells before and after reaction with a substrate; (g) improved in vitro solubility; (h) improved reactivity against O6-alkylguanine substrates; (1) reduced reactivity against DNA-based substrates; and (j) reduced reactivity against N9-substituted O6-alkylguanine substrates. Such AGT mutants with the mentioned improved properties are mutants wherein between 1 and 25 amino acids of the wild type human AGT are substituted by other amino acids, and optionally 1 to 5 amino acids out of the continuous chain at one, two or three positions are deleted or added and/or 1 to 4 amino acids at the N-terminus or 1 to 40 amino acids at the C-terminus are deleted. The invention further relates to a method for detecting and/or manipulating a protein of interest wherein the protein of interest is incorporated into a fusion protein with the AGT mutants of the invention. Another object of the invention are AGT fusion proteins comprising such AGT mutants and the protein of interest.