Non-covalent HaloTag Ligands for Fluorophore Stability
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Solution Overview
Problem
Current fluorescence microscopy techniques using HaloTag protein tags face limitations due to photobleaching of fluorophores, necessitating the development of non-covalent binding compounds and variants with enhanced specificity for prolonged imaging and improved fluorophore stability.
Innovation Solution
Development of non-covalently binding HaloTag compounds with specific linkers and variants that allow for reversible interaction with HaloTag proteins, utilizing moieties like methylamine, methylsulfonamide, and fluorinated analogues, and altering position D106 in the HaloTag sequence to change binding specificity, enabling prolonged imaging and improved fluorophore retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If covalent link between HaloTag protein and ligand is used, then stable protein labeling is achieved, but photobleaching of fluorophore occurs
Solution Approach 1:
The invention extracts the harmful covalent bonding mechanism and replaces it with non-covalent interactions. By removing the chloroalkane reactive group from the ligand structure, the patent eliminates the covalent link formation that leads to photobleaching, while maintaining stable protein labeling through high-affinity non-covalent binding
Solution Approach 2:
The patent employs a reservoir of unbound, non-photobleached fluorophores in the extracellular medium that continuously replace photobleached probes. This disposable approach uses abundant external fluorophore molecules to replenish the imaging pool, extending the duration of fluorescence imaging beyond the lifetime of individual fluorophore molecules
2Object-affected harmful factors
If non-covalent fluorescent ligands are used, then photobleaching is reduced, but binding specificity must be enhanced
Solution Approach 1:
The patent modifies specific local regions of the ligand molecule to optimize non-covalent interactions. By carefully designing the linker length (10-15 atoms) and terminal group chemistry (methylamine, methylsulfonamide, or fluorinated analogues), the invention creates localized interaction zones that maximize binding affinity and specificity without requiring covalent attachment
Solution Approach 2:
The invention systematically varies key molecular parameters including linker length (10-15 atoms), terminal group type (methylamine, methylsulfonamide, fluorinated analogues), and fluorophore characteristics to optimize the balance between binding affinity and photostability. These parameter adjustments enable non-covalent binding with sufficient specificity for imaging applications
3Duration of action of moving object
If prolonged image acquisitions are performed, then more biological information is obtained, but fluorophore stability decreases
Solution Approach 1:
The patent establishes a continuous replenishment system where unbound fluorophores in the extracellular reservoir continuously replace photobleached probes bound to the protein. This continuous action maintains a steady supply of fluorescent signals over extended periods, enabling prolonged time-lapse imaging and long-term tracking of protein dynamics
Solution Approach 2:
The invention introduces an intermediary exchange mechanism where extracellular fluorophore molecules act as mediators between the imaging system and the protein target. These intermediary fluorophores diffuse to the protein surface, replace photobleached probes, and maintain the fluorescence signal without requiring covalent attachment, thus extending imaging duration while preserving fluorophore stability
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
These non-covalent binding compounds and variants facilitate prolonged imaging by reducing photobleaching, enhancing the stability and specificity of fluorophores, and allowing for efficient labeling and localization of proteins, thereby improving the resolution and duration of fluorescence microscopy.
Implementation Method 1
non-covalently binding HaloTag compounds with specific linkers and variants that allow for reversible interaction with HaloTag proteins
Implementation Method 2
utilizing moieties like methylamine, methylsulfonamide, and fluorinated analogues, and altering position D106 in the HaloTag sequence to change binding specificity
Data Source
AI summary
A first aspect of the invention relates to a non-covalently-HaloTag-binding compound characterized by the general formula D-L-T (I), wherein D is or comprises a functional moiety Z, particularly a fluorescent dye, or D is a linkable moiety (i.e. a moiety that can be coupled to other functional groups), L is a linear linker of 10-15 atoms in length, and T is a moiety selected from the group comprising methylamine, methylsulfonamide, acetamide, or their respective fluorinated analogues, azide, or hydroxyl. Another aspect of the invention relates to a HaloTag variant wherein position D106 of the HaloTag7 sequence is exchanged for a proteinogenic amino acid different from D. The variant has a different binding specificity for HaloTag substrates compared to the non-variant Halotag polypeptide. Yet another aspect of the invention relates to kits comprising polypeptides or nucleic acids and the non-covalently-HaloTag-binding compound according to the invention.