EGFR antibody selection: total, phospho and the controls

Running a receptor signalling experiment

1. Decide whether the question is amount or activity. A total receptor antibody reports how much is present, which changes over hours to days. A phosphorylation-specific antibody reports activation at a residue, which changes in seconds to minutes. They answer different questions and a study usually needs both, on the same membrane.
2. Put phosphatase inhibitors in the buffer before you lyse. Phosphatases are active the moment a cell breaks. Inhibitors go into the lysis buffer fresh, the plate goes on ice, and the lysate is handled cold and quickly. Most missing phospho signal is lost in the first minute, and no amount of antibody optimisation recovers it.
3. Include a stimulated positive and an inhibited negative. Ligand-stimulated cells give a signal the antibody must detect, and cells treated with a selective inhibitor give a signal it must lose. That pair demonstrates both the reagent and the experiment, and a blot without them cannot show much.
4. Normalise phospho signal to total, not to a housekeeping protein. The informative quantity is the fraction of receptor that is phosphorylated, so the phospho signal is read against total receptor on the same samples. Normalising to a loading control alone confuses a change in activation with a change in abundance.
5. Check the residue and the species the antibody was raised against. Phospho antibodies are specific to a residue, and different residues report different downstream consequences. The residue number should be in your methods, and the sequence around it has to be conserved in your species for the reagent to work.

Time courses rather than single points

Receptor phosphorylation peaks within minutes and falls as the receptor is internalised and dephosphorylated, so a single time point can sit anywhere on that curve. A short time course is what makes a comparison between conditions interpretable.

Where the comparison is between cell lines, the kinetics themselves frequently differ, so matching a single time point between them compares the timing rather than the response.

Other readouts of the same question

Immunoassay formats measure phosphorylation quantitatively across many samples, and cytometry measures it per cell, which reveals whether a population responds uniformly or a fraction responds strongly. Both answer questions a blot cannot.

For surface receptor amount, flow cytometry on intact cells with an extracellular-epitope antibody is more informative than a blot, because it separates surface from total pools.

Buying EGFR antibodies as a pair

Buy total and phospho reagents from the same supplier where possible, so that the pair is validated together and the species reactivity claims are consistent. Record clone or catalogue number, lot and the residue for the phospho reagent.

Bank one lot of the phospho antibody for a study. These reagents are among the most lot-variable there are, and a change mid-study is indistinguishable from a change in biology.

Two questions, two shopping lists

A catalogue against this receptor contains reagents for at least three jobs: detecting the total protein, detecting a specific phosphorylation, and binding the receptor on live cells for blocking or sorting. Buying from the wrong part of that list is the most frequent cause of a signalling blot that cannot be interpreted.

Write the question down before searching. If the claim is that the receptor is present or amplified, you need a total reagent and a copy-number or message measurement. If the claim is that the pathway is on, you need a modification-specific reagent, the matching total, and a stimulated and an inhibited control.

A ctgf antibody and a secreted matricellular protein

CTGF is secreted and binds the matrix, so a ctgf antibody reports conditioned medium and tissue rather than a cytoplasmic pool, and the collection time and medium volume are part of the measurement. It is cleaved into fragments with their own activities, so the epitope decides which species is seen. Fibrotic tissue is the positive control the datasheet should show.

A shh antibody and a ligand that is processed and lipid modified

Sonic hedgehog is cleaved and then modified with a lipid at each end, so the active ligand is not the primary translation product and a shh antibody has to state which form it detects. Secreted forms travel in complexes, which makes medium a difficult sample. In tissue the informative readout is usually the pathway's target genes rather than the ligand itself.

A neuropilin-1 antibody and a co-receptor for two families

Neuropilin-1 serves both semaphorin signalling in neurons and growth factor signalling in endothelium, so a neuropilin-1 antibody is interpreted by tissue and by the partner receptor stained beside it. It is a large glycosylated membrane protein, so apparent mass sits above the calculated value, and a soluble form exists in plasma, which an extracellular domain clone will also detect.

A rage antibody and the isoform that is not a receptor

RAGE exists as the membrane receptor and as a soluble form that acts as a decoy, and the ratio between them is the readout in much of the literature, so a rage antibody has to say which it detects. Ligands are varied and low affinity, which makes functional work demanding. The glycosylated receptor runs as a broad band, and a deglycosylation lane is what shows that is the protein.

A klotho antibody and a protein measured in three forms

Klotho is a membrane protein whose extracellular domain is shed into blood and urine, and the clinical interest is mostly in that soluble form, so a klotho antibody for a section and an assay for the soluble protein are different purchases. Assays have historically disagreed, which is a reagent problem rather than a biological one, so the assay and its calibration belong in any figure.

A lipocalin-2 antibody and a marker that travels

Lipocalin-2, also called NGAL, is secreted and is measured in urine and plasma as an injury marker, so a lipocalin-2 antibody is usually part of an immunoassay and the sample handling dominates the result. It also forms a complex with a matrix protease, and some assays read the complex while others read the monomer. Which species the assay reports is the question to ask first.

An sstr2 antibody and a receptor read for a therapy decision

Somatostatin receptor 2 staining supports a treatment decision, so an sstr2 antibody is used with a scoring system and a validated clone rather than as a free choice, and membranous rather than cytoplasmic staining is what counts. The receptor internalises on ligand binding, which matters in treated samples. Imaging with a labelled ligand is the in vivo counterpart the stain is compared against.

Common questions

Why is there no signal from my phospho antibody?

Almost always sample handling. Phosphatases act within seconds of lysis, so inhibitors have to be in the buffer before lysis and everything kept cold and fast. A stimulated positive control tells you immediately whether the problem is handling or biology.

Should phospho signal be normalised to total receptor or to a loading control?

To total receptor on the same samples. The meaningful quantity is the fraction activated; normalising only to a housekeeping protein cannot separate more activation from more receptor.

Does the residue matter?

Yes. Different phosphorylation sites recruit different partners and report different downstream events, so the residue belongs in the methods and a result about one site should not be generalised to the receptor being active.

Can I strip and reprobe for total after phospho?

Commonly done and it costs signal and risks uneven stripping. Running duplicate membranes, or a fluorescent two-colour detection on one membrane, is more reliable where the ratio is the measurement.

Which reagent do I need for a signalling experiment?

Both: a modification-specific antibody and the matching total-protein antibody, read as a ratio, with a stimulated positive and an inhibited negative in the same run. A phospho blot alone cannot distinguish more signalling from more receptor.

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