Step by Step Validation
Validation of correct expression via Western blot
Figure 8: Western blot of different GFPs, using our own cell-free expressed expression mix and a commercial one.
After fluorescence analysis, we wanted to validate the expressed protein by performing a western blot. Of each finished cell-free expression reaction, we took 25 µl, performed a SDS-PAGE, blotted it onto a PVDF membrane and incubated it with anti-GFP antibodies. Detection was carried out with secondary HRP-labeled antibodies and ECL solution. The blot shows bands at the right height of about 30 kDa, with GFP being 28 kDa of size. This proves correct protein expression in our system. The Spy-GFP-His is slightly bigger, due to the SpyTag. As expected, no expression is visible in both negative controls. Our mix contains more lysate and therefore shows some smearing. The bands of the commercial kit are much lighter, almost invisible, correlating to its comparably weak expression level (see figure 6). The purified GFP smeared over a small range, but covers the range of our expressed proteins.