TR-PUBP Stabilizes Polyubiquitinated Substrates for Identification
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional methods are inefficient in identifying polyubiquitinated substrates due to rapid degradation by the proteasome and deubiquitination, making it difficult to isolate and identify these proteins using immunoprecipitation or other techniques.
Innovation Solution
Expressing a trypsin-resistant polyubiquitin-chain binding protein (TR-PUBP) in cells, which stabilizes the polyubiquitinated state of substrates and allows for efficient isolation and identification by coexpressing it with a ubiquitin ligase, followed by trypsin digestion and peptide analysis using anti-diGly antibodies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional immunoprecipitation methods are used to identify polyubiquitinated substrates, then the identification process can be performed, but the substrates are rapidly degraded by the proteasome and deubiquitinated, making isolation and identification difficult
Solution Approach 1:
The patent applies preliminary action by expressing the trypsin-resistant polyubiquitin-chain binding protein (TR-PUBP) before substrate degradation occurs. TR-PUBP binds to polyubiquitinated substrates in vivo, stabilizing them in a protected complex state that prevents proteasomal degradation and deubiquitination. This preliminary stabilization allows subsequent efficient isolation and identification of substrates that would otherwise be lost.
Solution Approach 2:
TR-PUBP serves as an intermediary protein that mediates between the polyubiquitinated substrate and the detection system. The trypsin-resistant nature of TR-PUBP allows it to protect substrates during processing, while its ubiquitin-chain binding capability enables specific capture of polyubiquitinated proteins. This intermediary function resolves the contradiction by providing both stability during isolation and efficiency in identification.
2Quantity of substance
If epitope-tagged ubiquitin is overexpressed in culture cells for comprehensive analysis, then mass spectrometry can be performed on immunoprecipitated proteins, but the number of kinds of ubiquitinated proteins that can be identified is extremely restricted
Solution Approach 1:
The patent extracts the essential function of ubiquitin binding from the complex overexpression system. Instead of overexpressing epitope-tagged ubiquitin and requiring complex immunoprecipitation workflows, TR-PUBP is designed to bind polyubiquitinated substrates directly in vivo through its ubiquitin-chain binding domains. This extraction of the core binding function simplifies the system while expanding substrate identification capability.
Solution Approach 2:
The patent changes the key parameter of trypsin resistance in TR-PUBP to enable stable isolation through trypsin digestion. While conventional methods use epitope tags requiring specific antibodies, TR-PUBP's trypsin resistance allows universal capture of polyubiquitinated substrates regardless of their specific ubiquitination sites, thereby increasing the diversity of identifiable proteins without requiring complex overexpression systems.
3Measurement precision
If mutant ubiquitin ligase without ubiquitin ligase activity is expressed to analyze binding proteins, then comprehensive binding analysis can be performed, but a large number of binding proteins that are not substrates are identified, making the method inefficient
Solution Approach 1:
The patent converts the potential harm of non-specific binding into a benefit by using TR-PUBP's specific trypsin resistance. While mutant ubiquitin ligases without activity identify many false-positive binding proteins, TR-PUBP expressed in wild-type cells captures only genuine polyubiquitinated substrates. The trypsin resistance serves as a selective marker that distinguishes true substrates from non-specific binders, converting the problem of binding specificity into a solution.
Solution Approach 2:
The patent replaces the mechanical system of co-immunoprecipitation with mutant ligases with a biochemical selection system using TR-PUBP's trypsin resistance. Instead of relying on physical binding interactions that produce many false positives, the method uses enzymatic resistance as a selective criterion. Only substrates that are genuinely polyubiquitinated and bound to TR-PUBP survive trypsin digestion, enabling precise and efficient substrate identification.
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 enables stable isolation and identification of polyubiquitinated substrates, improving the efficiency of substrate identification compared to conventional methods by preventing degradation and enhancing the detection of ubiquitination sites.
Implementation Method 1
An antibody which recognizes the ubiquitin signature is the anti-diGly antibody
Implementation Method 2
Trypsin cleaves the C-terminal of lysine and arginine
Implementation Method 3
a selective degradation system 'ubiquitin-proteasome system' established by proteasome that tracks the polyubiquitin chain as a target
Data Source
AI summary
An object of the present invention is to provide a method for efficiently identifying a polyubiquitinated substrate which is generally not easily identified. The method for identifying a polyubiquitinated substrate includes (1) a step of expressing a trypsin-resistant polyubiquitin chain-binding protein and a ubiquitin ligase in a cell, (2) a step of isolating a complex that contains the trypsin-resistant polyubiquitin chain-binding protein from the cell having undergone the step (1), (3) a step of subjecting the complex isolated by the step (2) to trypsin digestion, and (4) a step of identifying a peptide that has a ubiquitination site from a digested material obtained by the step (3).