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Dot-Blot method description


What solution can be applied in a dot?

Protein

Total protein is isolated in 1x PEB buffer prepared freshly from 4x stock (AGRISERA, AS08 300) according to Agrisera protocol (protease inhibitor coctail must be included). Protein amounts are determined using 1/5 of the volumes of the standard DC Protein assay (BIORAD) against a BGG standard dilution curve of 0.0, 0.2, 0.4, 0.6 and 0.8 mg/ml (plus a 0.5 mg/ml reference) prepared freshly from 2.0 mg/ml stock (PIERCE) in 1x PEB. Absorbances are red in triplicates against H2O. Variation of photometer readings should not exceed 5-10% and r2 of calculated standard curve should be > 0.995. Samples are stored aliquotted at -20ºC and used withing not longer than 6 months.
Recombinant protein
Pure recombinant protein in a dilution series.
Peptide
Peptide wihout KLH or BSA-conjugate, in a dilution series.

Blotting

An Immobilion-P Transfer PVDF Membrane (Millipore, Prod. No. IPV H00010, pore size 0.45 µm) is pre-wetted for 15 seconds in 100 % Methanol to allow membrane activation and then soaked in distilled water for 2 minutes followed directly by 5 minutes equilibration in TBS-T (20 mM Tris, 150 mM NaCl, 0.05 % Tween 20, pH 7.5). Do not let PVDF membrane to dry out. PVDF membrane is hydrophobic therefore applying pre-wetting protocol with methanol is necessary. No pre-wetting is necessary when using nitrocellulose membrane. A WHATMAN filter paper is soaked in TBS-T and placed on a dry WHATMAN filter paper on top of some paper towels. The PVDF membrane is placed on top of the filter stack and 2 µl of each protein is spotted within a pre marked grid. The membrane is then left to dry to fix the proteins to it for 1.5 h at RT.


Antibody incubation and signal detection

Non-specific sites are blocked with blocking solution (TBS-T with 2 % low fat milk powder or other blocking reagent) for 30 minutes at RT with agitation. Blocking solution is discarded and each membrane is incubated for 30 minutes with agitation with the desired dilution (1:500 to 1:50 000) of primary antibody in 10 ml of TBS-T containing 2% low-fat milk powder, followed by 3 x 5 minutes wash with TBS-T. Secondary antibody incubation is done with Alkaline phosphatase (ALP)-conjugated antibody (Agrisera recommended secondary antibodies,  anti-rabbit AS09 607, anti-goat AS09 630, anti-chicken AS09 606, anti-mouse AS09 629), at appropriate dilution suggested on a specific product info sheet. The membrane is washed with TBS-T 3 x 10 minutes before reaction development using alkaline phosphatase reagent BCIP®/NTB premixed solution (Sigma, Prod. No. B6404). Dot blot reaction can be also developed using ECL based reagents with appropriate secondary antibody, HRP (horseradish peroxidase) conjugated.


Application example



Dot blot reaction of anti-Fucose (Fuc) and anti-Xylose (Xyl) antibodies with various controls: Avidin (Fuc+/Xyl+), Fetuin (Fuc-/Xyl-), PLA2 (Fuc+/Xyl-) and Mur1-2 (Fuc-/Xyl+). 2 µl of protein (Avidin, Fetuin, PLA2) and 2 µl of protein extract from the mutant were  spotted on a nitrocellulose membrane, placed on top of 2 WHATMAN filters (one soaked in TBS-T) and dried for 1.5 h at RT. The membrane was blocked for 30 min with 2% low-fat milk powder in TBS-T (0.1% TWEEN 20) and incubated with anti-Fucose (1) (AS07 268, 1:1000) or anti-Xylose (2) (AS07 267, 1:1000) for 30 min and then with secondary anti-rabbit(1:1000) antibody (ALP conjugated secondary antibody AS09 607). Membrane was washed with TBS-T 3 x 10 minutes before reaction development using alkaline phosphatase reagent BCIP®/NTB premixed solution (Sigma, Prod. No. B6404).

Questions? Do not hesitate to contact Agrisera.