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Protein Protocols Protein Protocols

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1030 Hammerl et al.<br />

Fig. 1. Experimental setup for a cross-blot experiment: + and – indicate the position of the<br />

graphite electrodes of the semidry blotting apparatus. WS, stack of Whatman paper; DM, dialysis<br />

membrane; D-NC, donor blot NC sheet; R-NC, receptor blot NC sheet. The perpendicular<br />

orientation of the antigens bands on the blots to each other is indicated by arrows. The protein<br />

bands on the donor blot are faced downwards against the receptor blot, while the bands on the<br />

receptor blot are faced upwards against the donor blot.<br />

d. Place the donor blot, with the protein bands downward, onto the receptor blot in such<br />

a way that the bands on the donor blot are perpendicular to the bands on the receptor<br />

blot (see Note 9).<br />

e. Cover the donor blot with the dialysis membrane.<br />

f. Place the Whatman stack soaked with SBT onto the assembly and cover it with the<br />

cathodal plate of the semidry apparatus.<br />

4. Perform electrophoresis at a constant current of 3 mA/cm2 for 90 min (see Note 10).<br />

3.4.2. Reequilibration of the Receptor Blot<br />

1. Presoak two Whatman stacks of the same size as in Subheading 3.4.1., step 1 in PTS.<br />

2. Important note: During the following step, take extreme care not to slip the receptor blot<br />

against dialysis membrane! (See Note 11.)<br />

a. Disassemble the semidry apparatus.<br />

b. Remove the cathodal Whatman stack.<br />

c. Open the upper part of the dialysis membrane using a pair of forceps.<br />

d. Remove the donor blot and place into PBS-Tween.<br />

e. Close the dialysis membrane so that the receptor blot is completely wrapped in it.<br />

f. Place the receptor blot, wrapped in the dialysis membrane, between two Whatman<br />

stacks prewetted in PTS.<br />

g. Place this assembly into an appropriately sized tray and cover it with a glass plate and<br />

a weight of approx 50 g to stabilize it.<br />

h. Fill tray with additional PTS and incubate overnight without agitation.<br />

3.4.3. Immunostaining<br />

1. Remove the receptor blot from “reequilibration” assembly and wash all NC pieces (i.e.,<br />

donor blot, receptor blot, and reference strips) in PBS-Tween 3 × 10 min on a laboratory<br />

shaker (see Note 12).<br />

2. Incubate with enzyme-linked second antibody according to the manufacturer’s instructions<br />

(see data sheet) in PBS-Tween with 1 mg/mL of BSA.<br />

3. Wash blots as described in step 1.

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