Polysaccharide Nanocapsules for GPCR Screening
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Solution Overview
Problem
Current methods for selecting proteins that depend on complex intracellular synthesis or processing steps, such as G-protein coupled receptors (GPCRs), are inadequate as they lack the ability to maintain protein stability in detergent micelles, making it difficult to identify stable variants for research and industrial applications.
Innovation Solution
A method involving encapsulating bacterial cells with cationic and anionic polysaccharides to create detergent-resistant nanocapsules, allowing for the solubilization of GPCRs while retaining them inside, enabling the use of fluorescence-activated cell sorting (FACS) for selecting stable variants.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional selection methods (phage display, yeast display, bacterial display) are used to screen protein libraries, then large libraries can be examined rapidly, but proteins depending on complex intracellular synthesis or processing steps (such as GPCRs) cannot be selected because these methods cannot maintain protein stability in detergent micelles
Solution Approach 1:
The patent introduces an intermediary system (encapsulated cells with solubilized membranes) that mediates between the need for high-throughput screening and the requirement for maintaining complex intracellular proteins. The encapsulated cells serve as a bridge, allowing conventional FACS technology to screen for proteins that require intracellular synthesis and detergent solubility, thus expanding the applicability of high-throughput methods to GPCRs and similar complex proteins
2Quantity of substance
If bacterial display is used to select for high expression of GPCRs, then functional expression in E. coli is improved, but stability in detergent micelles is not sufficiently enhanced because the correlation between high expression and high stability is weak
Solution Approach 1:
The patent implements a feedback mechanism where cells are encapsulated, solubilized with detergent, and then subjected to FACS sorting based on fluorescence signal from ligand binding. This feedback loop allows selection of variants that simultaneously exhibit high expression levels and high stability in detergent micelles, as only stable, functional proteins will produce sufficient fluorescent signal to be selected. The process iteratively enriches for dual-optimized variants
3Ease of operation
If cells are solubilized with detergent to allow entry or departure of small molecules, then ligand binding assays can be performed, but the cell membrane is disrupted which traditionally destroys the genotype-phenotype linkage
Solution Approach 1:
The patent uses a flexible polysaccharide capsule shell that can be reversibly disrupted by detergent to allow ligand access, then reformed to maintain containment. This flexible shell approach enables temporary membrane disruption for ligand binding assays while preserving the encapsulated cell's integrity and genotype-phenotype linkage throughout the selection process. The capsule acts as a controllable barrier that can be opened for assays and closed for selection
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 method allows for the direct selection and isolation of detergent-stable GPCR mutants, enhancing their stability and functional expression, facilitating their use in biophysical studies and crystallography, and potentially other membrane proteins, by maintaining the genotype-phenotype linkage during the selection process.
Implementation Method 1
a plurality of cells is encapsulated in an encapsulating step, wherein cells are treated with a cationic polysaccharide ('cationic treatment step') and with an anionic polysaccharide ('anionic treatment step')
Implementation Method 2
the encapsulated cells are solubilized ('solubilization step') so that their membrane is disrupted to allow for the entry or departure of small molecules (low molecular mass compounds such as oligopeptides) into the cell or out of the cell
Implementation Method 3
the solubilized compartments are contacted with a ligand to said target protein, wherein the ligand bears a detectable label
Data Source
AI summary
The invention relates to a method for selecting a sequence set from a library of expressed nucleic acid sequences, wherein cells are provided, each cell comprises an expressed nucleic acid sequence expressed as a target protein. The cells are encapsulated by treating them with a cationic polysaccharide and subsequently treating them with an anionic polysaccharide, yielding encapsulated cells, perforating the membrane of the encapsulated cells, yielding solubilized compartments, contacting them with a ligand to said target protein, the ligand bearing a detectable label, and selecting a subset of solubilized compartments as a function of detectable label and isolating the expressed nucleic acid sequences from the selection as a selected sequence set.