Dear Mohammed,

principally, I would not expect problems. Do you have any idea in which kind of buffer (salt content/ionic strength, detergents, chaotropic salts) your proteins are in? If in doubt, dilute your proteins as much as possible (possibly you might want to run an initial dilution experiment first, in order to determine a reasonable dilution window for your samples).

If SDS was involved in lysing your tissue, then the proteins might react differently compared to native proteins, as they might stay denatured.

One thing I strictly would avoid in the elution buffer are reducing agents (BME, DTT, TCEP) as they will kill any antibody they get in contact with and thus render your ELISA probably nonfunctional.

Have you already tried or are you just planning your experiment?

Best regards,

Wolfgang

Dear Wolfgang,

thank you for the offer to help. To answer your questions;

1. The protein was isolated using a kit (Biorad) and sometimes one cannot be too sure what substances some of their extraction solution contains. However, the lysis was done with a solution they call RP1 mixed in a ratio 10: 1 with mercapto ethanol and a little of DTT was added. It was passed through a sieve, its binding condition of which was adjusted with 70% Ethanol to facilitate binding of RNA. The protein was precipitated with what they call PP (protein precipitate), again cannot say what it is (may be a chelator?). Then the protein precipitate was washed with ethanol 3 times, abd then solubilized in a buffer (protein solubilising buffer mixed with TCEP, PSB-TCEP), cannot say what it is either. However, the buffer is said to function like laemli buffer, since the protocol said there was no need to add laemli before running a SDS-PAGE, it is also blue in color. That is it.

2. I am not sure if SDS was not used in the lysis. I was going to run SDS-PAGE anyway, to verify if my protein of interest would show a band.

3. I have the protein and have not yet run the ELISA, just planning. I have a pre-coated plate of the primary antibody and all the other reagents.

4. By dilution, what conc. would you advise I aim for?

5. Since very little (2 micro liter of 0.05 molar to 30 mg tissue ground in 350 micro liter buffer) DTT was used during tissue lysis, would the dilution really reduce the effect of the DTT or does it mean its a hopeless case?

Thanks again

Dear Mohammed,

I'd assume that the protein dissolution buffer contains SDS and a reducing agent, when it may be used directly for SDS-PAGE. Not suitable for ELISA.

Try to dissolve the pellet that you get after the EtOH wash, you might perform another wash with a little ether to get rid of the Ethanol, the pellet needs to be free of Ethanol and other solvents, (leave it a few hrs to overnight at room temperature or 37degC, cover the vials with a tissue, but do not apply vacuum or heat) and dissolve the protein pellet in PBS containing a litte (0.1% m/v) Tween 20 (=PBST). This may take awhile, an ultrasound bath (those from the IMPEX-shops near the train station sold for cleaning glasses will do perfectly) may be helpful in difficult cases. Then make a few serial dilutions (10x is good for a start) in the same buffer and use this for your ELISA. If you have no idea how much of the analyte is present in your samples, for a start, use a definitely strongly positive sample (or spike a sample with an expected concentration) and determine a dilution where the signal is within the standard curve of the ELISA

.

Thanks so much. However it means I would need to recover the protein since I already dissolved it in the PSB-TCEP (the protein solubilization buffer. I will take an aliquot of it, recover the protein pellet and proceed as you have advised. Will let you know how it goes and possibly ask for more help.

Thanks again

Try again to pecipitate (Ethanol or even TCA or perchloric acid).

If this does not work, you could try desalting: Probably a small spin column like NAP10, Zeba sth,. or so will do best. A problem that might arise is a somewhat uncontrolled dilution of your samples and binding on the column, so you will need to determine recovery. A further problem might be possible micelle formation that lowers the efficienty of the process. Blocking the columns with eg BSA is recommended.

Maybe adding a colored big molecule (like commercial dye-coupled dextrane, as sold for standardization of analytical gel filtration) or a homemade colorful BSA (simply make an azo coupling to BSA, chemists near you can help) to the sample and measuring the recovered material in a photometer.

Dear Mohammed,

Nucleospin kit is actually designed for Western blot analysis and denaturate and reduces proteins completely. Even after dialysing and or reprecipation is not easy to use the protein for ElISA. I would suggest to try Western blots with antibodies recognizing the denatured and reduced protein.

Good Luck

Hi Behrouz, this is a completely interesting NEWS to me and thank you so much!

I bought the 50 preps and only used 8 but seems like a waste of money already.

I got quite some interesting suggestions here like yours and would adapt as the case may be. Thank you for this vital information.

Quantification by western blotting is possible, but not easy, due to the low linear response of Chemiluminescence / Xray film that normally is used. From this, you may deduce qualitative conclusions, however.

If you really want to quantify, you'll need access to more sophisticated equipment, e.g. a high dynamic CCD camera system for integrating the chemiluminescence signal or a scanner for fluorescently labelled secondary antibodies (eg the Licor Odyssey).