Ubiquitin antibody and other modification state reagents: detecting a state, not a protein

Getting a modification blot to work

1. Inhibit the removing enzymes at lysis. Deubiquitinases, phosphatases and other erasers remain active in a cold lysate and strip the modification within minutes. The inhibitor has to be in the buffer before the cells meet it, not added afterwards.
2. Choose the reagent by linkage and by state. Some antibodies recognise the modifier regardless of context, some recognise a specific chain linkage, and some recognise the modified form of one target protein. These answer different questions and are frequently sold under similar names.
3. Expect a distribution, not a band. Poly modified proteins run as a ladder or a smear because chain length varies. A clean single band from a general reagent is more likely to be a cross reaction than a result.
4. Enrich when the fraction is small. Only a small proportion of a target is usually modified at any moment. Immunoprecipitation of the target followed by modification blotting, or capture with a binding domain reagent, is often the only way to see it.
5. Control with a treatment that changes the modification. An inhibitor or stimulus that raises or lowers the modification is the control that proves the signal is the modification. An untreated lane alone proves nothing about specificity.
6. Record the clone and the lysis buffer together. For this class of reagent the buffer is as much part of the method as the antibody. Keep them recorded as a pair, because a protocol that omits the inhibitor cocktail will not reproduce.

The buffer is half the reagent, and an anti-ubiquitin antibody is the other half

For modification detection, what happens in the first two minutes of lysis determines whether there is anything to detect. Inhibitors in the buffer, cold everything, and a short path from plate to denaturation are the whole technique.

Laboratories that standardise a single modification lysis buffer, made fresh with inhibitors and dated, stop having this class of failure almost entirely.

Validating a modification antibody, k63 ubiquitin antibody included

The strongest validation is a treatment that moves the modification in a known direction, ideally in both directions, with the total protein unchanged. Genetic removal of the modification site is stronger still where it is feasible.

A supplier's blot on an overexpressing lysate is not validation for your system. Run the treatment control once per clone and keep the image with the reagent record.

Degrader experiments, and where a k48 ubiquitin antibody is the readout

A targeted degradation experiment makes three separate claims: the target falls, the effect depends on the machinery, and the machinery component is present and engaged. Each needs its own reagent, and the component antibodies are typically raised against proteins far scarcer than the target itself.

Budget for that asymmetry. The reagent against the ligase component is usually the limiting one, and confirming that it detects the endogenous protein rather than only an overexpressed tagged version is the check most often skipped and most often responsible for a result nobody can interpret.

Loading controls that are not controls

Proteins used as loading controls are chosen for abundance and assumed stability, and both assumptions fail under exactly the treatments a turnover experiment uses. A control loaded far above the linear range cannot show a difference in loading at all, which makes it worse than none.

Total protein staining of the membrane measures what was loaded rather than one protein's response to the treatment, and it is the more defensible control here. Where a single protein is used, keep it inside its linear range and choose one with no known relationship to the pathway under study.

One gene, two accepted symbols

Several genes in this area carry more than one accepted symbol, and a catalogue search on one of them returns only part of the available reagents. Searching on the gene identifier rather than the symbol, and comparing immunogen sequences rather than product names, is what stops you comparing a fraction of the market against itself.

The same applies when reading the literature for a reagent's track record. Two bodies of published work can sit under two symbols for one protein, and the unhappy experience with a reagent is as likely to be recorded under the spelling you did not search.

A nedd8 antibody and a different modifier

NEDD8 is a ubiquitin like protein that modifies cullin ligases rather than marking proteins for degradation, so a nedd8 antibody answers a different question from a ubiquitin one and the two should not be read as interchangeable. An inhibitor of the activating enzyme is the functional control that collapses the signal, and free and conjugated forms run at different masses.

A nedd4 antibody and a ligase family

NEDD4 is an E3 ligase family whose members share domains, so a nedd4 antibody has to state which member and what it was tested against, and the readout of interest is a substrate's ubiquitination or level rather than the ligase's own abundance. The protein is large, so transfer matters, and a knockdown lane makes the band attributable.

A huwe1 antibody and a very large ligase

HUWE1 is an unusually large E3 ligase, so a huwe1 antibody needs a low percentage gel and a long transfer and a missing band is usually the transfer. Its substrates span several pathways, so the figure has to name which substrate is being followed. Its own level is stable, which is why a substrate readout rather than the ligase is the measurement.

Common questions

Why is my ubiquitination antibody blot a smear?

Because chain length and site occupancy vary across the population, which produces a distribution rather than a band. For poly modified targets that smear is the correct result and quantifying it means integrating the region rather than picking a band.

Why did the signal disappear?

Almost always active removing enzymes during lysis. The inhibitor must be present in the buffer before lysis, samples kept cold and processing kept short. Warm handling for a few minutes is enough to lose the signal.

Do I need a linkage specific reagent?

Only if the linkage is the question. For a general question about whether a target is modified, a pan reagent with a good enrichment step is usually the practical route, with a linkage specific reagent to follow up.

Can I strip and reprobe for the total protein?

It is common and it is risky, because stripping removes target as well as antibody. A duplicate membrane or fluorescent multiplexing gives a more defensible total protein comparison.

Why does a partial degradation look complete on my blot?

Usually because the antibody was saturated or close to its detection limit at the starting level. Establish the linear range with a lysate dilution series first; outside it the blot reports the assay rather than the biology.

Which lysis buffer should a turnover experiment use?

It depends on the question. Harsh conditions release a protein from its complex and gentle ones keep it bound but may not solubilise it, so measuring the protein and measuring its partners call for different buffers. Using the laboratory default for both gives two different kinds of wrong answer.

Browse by service class

• Compare Gene synthesis on advertised prices