Peptide Scanning-assisted Identification of a Monoclonal Antibody-recognized Linear B-cell Epitope

The overall goal of this protocol is to identify a monoclonal antibody-recognized linear B-cell epitope using serially truncated recombinant proteins and peptide scanning by dot-blot hybridization. This method can help answer key questions concerning the molecule interaction between antigen and the antibody. The main advantages of this technique are its simplicity and efficiency.

The identifying epitope can then be used in fuller investigations such as in therapeutical and diagnostic applications. Demonstrating the procedure will be Chien-Wen Chen, a post doctorate from my laboratory. To begin, grow RGM56 mouse monoclonal hybridoma cells in a hybrid serum free medium.

Maintain cell cultures in 175 T flasks at 37 degrees Celsius 5%carbon dioxide. After five days of incubation, collect the culture medium after it has turned yellow and centrifuge the supernatant at 4, 500 times G for 30 minutes at four degrees Celsius. Then, discard the pelleted cell debris to obtain the antibody in solution.

Next, add two milliliters of 50%protein G agro slurry to a five milliliter column and equilibrate the resin with 10 milliliters of ice cold PBS, equaling 10 volumes of preloaded resin. Load 200 milliliters of the previously prepared antibody solution onto the equilibrated column and discard the fraction that passes through the column. Using 10 milliliters of ice cold PBS, wash the column twice.

Finally, to loot the antibody from the resin, add 10 milliliters of millimolar glycerin solution at pH 2.7 to the column. Collect 900 microliter fractions in microcentrifuge tubes previously filled with 100 microliters of 10X neutralization buffer. Store the purified antibody in 50%glycerol solution supplemented with sodium azide at minus 20 degrees Celsius.

Prepare the constructs and transform E.coli BL21 cells as described in the text protocol. Then, transfer a single colony into a 15 milliliter tube containing three milliliters of LB broth supplemented with 100 micrograms per milliliter ampicillin and loosely cap the tube. Incubate the culture at 37 degrees Celsius with 150 RPM shaking.

Monitor the optical density of the culture at 600 nanometers. When it reaches about 0.6, cool the culture to 25 degrees Celsius. Then, add IPTG at a final concentration of 0.4 millimolar to induce the expression of the recombinant protein.

Incubate the culture for another four hours at 25 degrees Celsius with 200 RPM shaking. After incubation, transfer one milliliter of the bacterial culture into a microcentrifuge tube. Centrifuge the cells at 12, 000 times G for one minute and discard the supernatant.

Pipetting up and down with a micropipette, resuspend the cell pellet in 100 microliters of denaturation buffer. And mix the resulting suspension by vigorous vortexing to obtain a ready to use recombinant protein sample. To proceed with dot-blot hybridization, dissolve each synthetic peptide in DMSO to obtain 10 milligram per milliliter solutions.

Then, activate the PVDF membrane in methanol for two minutes and equilibrate it with modified Towbin buffer for another two minutes. Rinse a piece of chromatography paper with modified Towbin buffer and lay the equilibrated PVDF membrane on it. Let the membrane sit until the buffer disappears from its surface.

Using a 10 microliter tip, add two microliters of each peptide or recombinant protein sample onto the membrane and let it air dry for 10 minutes. Spotting a symbol onto the membrane is the most critical step in this protocol. Loading a precise amount of a sample onto a small area of the PVDF membrane needs careful attention.

Next, block the membrane in TBST buffer supplemented with 5%nonfat milk for 30 minutes at room temperature with gentle shaking. Dilute the RGM56 monoclonal antibody in TBST buffer supplemented with 5%nonfat milk. And add the antibody solution to the membrane.

Incubate the membrane at 37 degrees Celsius for one hour with gentle shaking. After incubation, remove the antibody solution. And wash the membrane twice in TBST buffer for five minutes with gentle shaking.

Then, add to the membrane the solution of the secondary antibody diluted in TBST buffer with 5%nonfat milk. Incubate the membrane for one hour at 37 degrees Celsius with gentle shaking. Upon incubation, discard the antibody solution and wash the membrane in TBST buffer twice for five minutes with gentle shaking.

Then, develop the membrane with the substrate solution at room temperature for 15 minutes in the dark. When the signal appears, stop the reaction by washing the membrane with doubly distilled water. After air drying the membrane, capture the dot-blot image using an imaging system.

Finally, using image analysis software measure the intensity of each dot-blot. Presented here is the full length nervous necrosis virus code protein comprising amino acids one through 338 along with its serially truncated variants. To confirm the expression of the proteins in the transformed bacterial cells, dot-blot analysis using anti-6XHis antibody was performed showing the presence of all the proteins under investigation.

Then, the recombinant proteins were analyzed by dot-blot hybridization in which the RG-M56 monoclonal antibody was used. The analysis revealed that the protein epitope recognized by the antibody is found in peptide 195 to 338. Finally, an epitope consisting of 20 or eight amino acid residues was identified by peptide scanning.

Alanine scanning showed that substitutions of valine residues at positions 197 and 199 as well as a cystine at 201 abolished the epitope's binding capability and dot-blot hybridization. Similarly, the decreased binding affinity was observed in binding intensity analysis confirming that the identified residues are essential for the epitope's binding to the RGM56 monoclonal antibody. This peptide identification technique can be used to develop therapeutical peptide drugs or peptide medicines.