Ubiquitin Ligase (E3) Activity Profiling

Ubiquitin Ligase (E3) Activity Profiling – From Auto‑ubiquitination to Substrate Modification and High‑Throughput Screening

If you are searching for ubiquitin ligase (E3) detection services, you likely need to measure the enzymatic activity of a specific E3 ligase, identify its ubiquitination substrates, determine E2‑E3 pairing preferences, or screen for inhibitors/activators in drug discovery projects. E3 ligases are critical for protein homeostasis, cell signaling, and are emerging as therapeutic targets (e.g., PROTACs). Our laboratory provides comprehensive ubiquitin ligase analysis – from in vitro auto‑ubiquitination assays and substrate ubiquitination kinetics to E3‑E2 binding characterization, high‑content cellular assays, and proteome‑wide substrate identification – using recombinant proteins, cell lysates, and advanced mass spectrometry platforms.

What We Analyze – Full Ubiquitin Ligase Activity Scope

We do not simply report “active or inactive”. Our platform includes in vitro ubiquitination reconstitution assays using purified E1 (e.g., UBE1), E2 (selected from a panel of ~40 human E2s), and E3 ligase (your protein) with wild‑type or mutant ubiquitin (e.g., K‑only, zero‑lysine). Activity is quantified by Western blot (anti‑ubiquitin, anti‑HA/His if tagged) or high‑sensitivity AlphaScreen/TR‑FRET using ubiquitin‑specific antibodies. For kinetic parameters, we perform time‑course and concentration‑dependent assays to determine k_cat, K_M, and catalytic efficiency. We also measure E2‑E3 binding affinity (K_D) by SPR or MST. For substrate ubiquitination, we incubate E3 with purified substrate protein (or peptide) and quantify multi‑monoubiquitination or polyubiquitin chain formation (linkage‑specific by using linkage‑specific antibodies or MS). To identify unknown substrates, we perform in vitro ubiquitination reactions followed by LC‑MS/MS to map ubiquitination sites on candidate substrates or on the E3 itself (auto‑ubiquitination sites). In cellular contexts, we use co‑immunoprecipitation (co‑IP) plus Western blot or ubiquitin‑remainder profiling (diGly remnant enrichment with LC‑MS/MS) to identify E3‑dependent ubiquitination events. For high‑throughput inhibitor screening, we offer 384‑well format TR‑FRET or AlphaLISA assays with Z' >0.6, ready for compound library screening.

Key parameters and deliverables we routinely provide:
- E3 auto‑ubiquitination activity (intensity, polyubiquitin ladder pattern) – qualitative or semi‑quantitative.
- Substrate ubiquitination efficiency (e.g., % substrate modified, ubiquitin conjugation rate) – from densitometry or MS.
- Kinetic constants (k_cat, K_M) for substrate or ubiquitin conjugation – CV <20%.
- E2 selectivity profile (which E2s support ubiquitination with given E3) – heatmap of relative activity.
- Binding affinity between E3 and E2 or substrate (K_D) – by SPR or MST.
- Ubiquitin chain linkage determination (K48, K63, K11, linear, etc.) – using linkage‑specific antibodies or MS.
- Identification of ubiquitination sites on substrate (by LC‑MS/MS) – with localization probability >0.9.
- IC₅₀ values for E3 inhibitors (e.g., MLN4924, PROTAC modulators) – with positive/negative controls.
- Cell‑based E3 activity (e.g., degradation of known substrate by Western blot, or using reporter construct) – with proteasome inhibitor validation.

How Deep We Go – Multi‑E2 Profiling, Linkage‑Specific Quantification, and Proteome‑Wide Substrate ID

Most routine E3 activity labs test only one or two E2s and rely solely on Western blot. We provide a panel of 40+ recombinant human E2 enzymes to match the specific E3 (e.g., UBE2D family for RING E3s, UBE2C for APC/C, UBE2T for FANCL). For linkage‑specific polyubiquitin chain analysis, we combine linkage‑specific antibodies (for K48, K63, K11) with fluorescence detection and LC‑MS/MS using tryptic ubiquitin remnant (diGly) with linkage‑type quantitation via signature peptides. For proteome‑wide substrate discovery, we use quantitative ubiquitin‑remainder proteomics (diGly‑LC‑MS/MS) in cells with E3 overexpression vs. knockdown, or with a chemical inhibitor, identifying hundreds of potential E3 substrates with fold changes and statistical significance. We also perform in vitro ubiquitination coupled with mass spectrometry (IV‑Ub‑MS) to directly map ubiquitination sites on candidate substrates and assess processivity. For drug discovery support, we validate hits in orthogonal cellular assays (e.g., NanoBRET target engagement for PROTACs, or degradation assays by HiBiT tagging).

Advanced capabilities include:
- Real‑time ubiquitination kinetics using time‑resolved FRET (TR‑FRET) in 384‑well format – ideal for HTS.
- Single‑molecule ubiquitination assay (smUb) to detect rare or distributive ubiquitination events.
- E3 ligase autoubiquitination site mapping (by MS) to understand regulatory mechanisms.
- Cross‑linking mass spectrometry (XL‑MS) to map E3‑E2‑substrate interaction surfaces.
- Biolayer interferometry (BLI) for rapid E2‑E3 binding screening.
- In vitro deubiquitinase (DUB) resistance assay to test chain stability.
- High‑throughput E2‑conjugating enzyme activity screening for E3 ligase specificity profiling.

We routinely achieve measurement sensitivities: in vitro auto‑ubiquitination detected from 1 ng E3; substrate ubiquitination IC₅₀ CV <15%; MS identification of ubiquitination sites with Ascore >95%; Z' factors >0.6 for screening assays. All methods follow NIH/NCATS guidelines for ubiquitination assays and standard practices for ubiquitin biochemistry.

Why Choose Our Ubiquitin Ligase Testing – Key Advantages

1. ISO/IEC 17025:2017 accredited and GLP‑compliant workflows – data suitable for target validation, SAR studies, and preclinical drug discovery.
2. Comprehensive E2 panel (40+) to match physiological E3 partners – we identify the optimal E2 for your E3, avoiding false negatives.
3. Linkage‑specific ubiquitin chain analysis (K48/K63/K11/linear) by orthogonal methods (antibody + MS) – critical for understanding downstream signaling.
4. Proteome‑wide substrate discovery (diGly‑MS) integrated with in vitro validation – we go from hypothesis to specific ubiquitination sites.
5. High‑throughput screening capability (384‑well, Z’>0.6) – ready for compound libraries.
6. Fast turnaround with full data transparency – E3 auto‑ubiquitination and E2 profiling in 5‑7 business days; substrate identification and MS mapping in 10‑12 business days. You receive raw Western blots, kinetic curves, MS spectra, and a complete activity report.
7. Custom development for orphan or novel E3 ligases (including multicomplex E3s like APC/C, SCF, CUL3) – we help reconstitute complexes and design assays.
8. Competitive pricing for complete E3 characterization packages – bundling E2 profiling, substrate ubiquitination kinetics, linkage analysis, and cellular validation costs 30‑35% less than separate services.

We have successfully completed over 200 E3 ubiquitin ligase projects for pharmaceutical companies, biotech startups, and academic drug discovery groups. Our team includes PhD biochemists and cell biologists with deep expertise in ubiquitin‑proteasome system.

Ready to Test Your Ubiquitin Ligase Activity?

Provide your E3 ligase name, available reagents (recombinant protein, lysate, or cDNA), and your objective (e.g., “measure auto‑ubiquitination”, “identify substrates”, “screen inhibitors for RNF43”). We will provide a free technical consultation, a tailored assay design, and a fixed‑price quote. Whether you need a simple activity confirmation or full substrate and inhibitor profiling, we deliver deep, accurate, and biologically relevant ubiquitin ligase testing tailored to your drug discovery or research program.