Ubiquitin Chain Length Determination via Trypsin Protection
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Solution Overview
Problem
Current methods lack a practical technique for determining the actual chain length of endogenous ubiquitylated substrates, which is essential for understanding the biological significance of different ubiquitin chain topologies and complexities.
Innovation Solution
A polypeptide comprising ubiquitin binding domains linked via a trypsin-resistant linker amino acid sequence, specifically the TR-TUBE, is used to protect ubiquitin chains from trypsinization, allowing for the analysis of ubiquitin chain length by affinity capture and subsequent western blotting or mass spectrometry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If gel mobility shift analysis is used to analyze ubiquitin chain length, then the method is simple and quick, but it cannot accurately determine the actual chain length of endogenous ubiquitylated substrates due to heterogeneous chain lengths and multiple ubiquitylation sites
Solution Approach 1:
The method segments the ubiquitin chain analysis by using trypsin to selectively digest the substrate protein while leaving the ubiquitin chain intact, then uses affinity capture to isolate and analyze only the ubiquitin chain portion, effectively separating the measurement of substrate from the measurement of ubiquitin chain length
Solution Approach 2:
The patent introduces an affinity probe (such as anti-ubiquitin antibody or ubiquitin binding domain-containing protein) as an intermediary to capture and concentrate the ubiquitin chains from the complex cellular mixture, enabling precise measurement of chain length without interference from multiple ubiquitylation sites on different substrates
2Measurement precision
If affinity capture with trypsin-resistant polypeptide is used to protect ubiquitin chains from trypsinization, then the chain length can be accurately determined, but the device complexity and procedure steps increase
Solution Approach 1:
The method applies preliminary anti-action by using trypsin-resistant polypeptides (such as TUBE or TR-TUBE) that specifically bind to and protect ubiquitin chains from trypsin digestion before the chain length analysis, preventing the degradation of the ubiquitin chain structure that would otherwise occur during the measurement process
Solution Approach 2:
The patent performs preliminary action by pre-incubating the ubiquitylated substrate with the affinity probe (TUBE/TR-TUBE) before trypsin treatment, allowing the probe to capture and protect the ubiquitin chains in advance, which simplifies subsequent analysis steps
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 method effectively determines the mean length of substrate-attached polyubiquitin chains and reveals the robustness of ubiquitin length regulation in cells, providing insights into the functional units of ubiquitin chains and their roles in cellular processes.
Implementation Method 1
a polypeptide comprising ubiquitin binding domains... useful for the method for determining ubiquitin chain length
Implementation Method 2
digesting the mixture with a protease to form a digested mixture... protected from trypsinization
Data Source
AI summary
Protein ubiquitylation, an essential post-translational modification, regulates almost every cellular process including protein degradation, protein trafficking, signal transduction, and DNA damage response in eukaryotic cells. The diverse functions of ubiquitylation are thought to be mediated by distinct chain topologies resulting from eight different ubiquitin linkages, chain lengths, and complexities. Currently, ubiquitin linkages are generally thought to be a critical determinant of ubiquitin signaling. However, ubiquitin chain lengths, another key element of ubiquitin signaling, have not been well documented especially in vivo situation during past three decades from the discovery of ubiquitin. The reason of this was simply because no method has been available for determination of ubiquitin chain length in endogenous ubiquitylated substrates. In the present invention, a practical technique for determining the actual length of substrate-attached polyubiquitin chains from biological samples is established. Using the method, the mean length of substrate-attached polyubiquitin chains was determined and the robustness of ubiquitin chain length regulation in cells is investigated. The following is a summary of findings in this invention: 1. A method for determining ubiquitin chain length was developed and this method was named ‘ubiquitin protection from trypsinization’ (Ub-ProT). 2. Using Ub-ProT, it was determined that the mean length of substrate-attached ubiquitin chains is in the dimer to decamer range. 3. By quantitative proteomics, it was found that the mean lengths of five major types of ubiquitin chains can be divided into two groups. 4. Proteasome-inhibition did not alter the mean length of substrate-attached polyubiquitin chains, indicating that cells have a robust system for regulating ubiquitin chain length.