Engineering pH-Sensitive Protein Switches via Internal Ionizable Residues
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Solution Overview
Problem
Engineering artificial pH-sensitive conformational switches within proteins is challenging, particularly in introducing ionizable amino acid residues that can respond to small pH changes without destabilizing the protein, as naturally occurring pH sensors rely on surface ionizable residues and modifying internal ionizable groups is difficult.
Innovation Solution
Introducing ionizable amino acid residues with shifted pKa values into the hydrophobic interior of proteins, such as Lys, Asp, and Glu, to create artificial pH-sensitive switches that undergo global unfolding in response to pH changes within a specific pH range, allowing for cooperative transitions between folded and unfolded states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If ionizable amino acid residues are introduced into the hydrophobic interior of proteins to create pH-sensitive switches, then the protein can respond to pH changes with conformational transitions, but the protein stability is compromised due to the incompatibility of charged species with the hydrophobic environment
Solution Approach 1:
The patent introduces ionizable residues at specific local positions within the hydrophobic core where they can form favorable interactions (such as salt bridges or hydrogen bonds) with nearby residues. This localized placement allows the charged species to be stabilized in the hydrophobic environment, enabling pH sensitivity without compromising overall protein stability. The key is selecting specific sites where the hydrophobic environment can be locally modified to accommodate charged groups.
Solution Approach 2:
The patent uses intermediate residues or structural elements that mediate between the ionizable group and the hydrophobic environment. These intermediaries can shield the charged group from the unfavorable hydrophobic environment or provide alternative stabilization pathways, allowing the pH-sensitive residue to function without destabilizing the overall protein structure.
2Adaptability or versatility
If His residues are introduced as pH sensors in natural proteins, then the protein can undergo pH-driven conformational transitions, but engineering artificial pH sensing proteins by introducing His residues is challenging due to difficulty in controlling pKa values and achieving desired sensitivity
Solution Approach 1:
The patent systematically varies multiple parameters including the type of ionizable residue (Asp, Glu, Lys, Arg, His), the position within the hydrophobic core, and the surrounding amino acid environment to achieve desired pKa values and pH sensitivity. By changing these parameters, the patent can tune the pH response characteristics of the engineered proteins to match specific applications.
Solution Approach 2:
The patent employs multiple types of ionizable residues (not just His) to create pH sensors, making the engineering approach more universal and versatile. Different residue types offer different pKa ranges and sensitivity profiles, allowing the selection of optimal residues for different pH ranges and applications, thereby reducing the challenges associated with His-specific engineering limitations.
3Reliability
If internal ionizable groups are present in proteins, then they can play essential roles in energy transduction processes, but charged species are not compatible with the hydrophobic and dry interior of proteins
Solution Approach 1:
The patent segments the hydrophobic core into regions with different properties, creating localized pockets or environments that can accommodate charged species. By dividing the interior space, the patent can place ionizable groups in specific segments where they can perform energy transduction functions while being shielded from the unfavorable bulk hydrophobic environment by surrounding residues or structural features.
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
This approach enables the design of proteins that respond to physiological pH changes with significant conformational rearrangements, enhancing their stability and solubility while maintaining thermodynamic stability, and can be used to engineer pH-sensitive proteins for biotechnological applications.
Implementation Method 1
the one or more ionizable amino acid residues titrate with a pKa value shifted relative to the normal pKa value in water for the one or more ionizable amino acid residues
Implementation Method 2
charged species are not compatible with the hydrophobic and dry interior of proteins
Implementation Method 3
folding landscapes are usually dominated by the fully folded and the unfolded states... partially unfolded proteins are unstable relative to fully folded proteins
Data Source
AI summary
Methods are provided for engineering non-naturally occurring proteins comprising artificial pH-sensitive conformational switches that respond to a change in pH by causing a global unfolding of the proteins. Non-naturally occurring proteins comprising artificial pH-sensitive conformational switches that respond to a change in pH by causing a global unfolding of the proteins are also provided.