SPINE

SPINE is a method to detect in vivo protein-protein interactions PubMed

A detailed protocol to detect the interaction between RocG and GltC:

1 litre of a B. subtilis culture was grown to an OD₆₀₀ of approx. 1.0 and incubated with 0.6% formaldehyde ( 4% stock solution in PBS, pH 6.5!) for 20 minutes @ 37°C on a shaker. The cells were harvested and washed once in 1 X PBS pH 6.5. The pellets can then be stored @ -20 °C. The GltC protein was expressed carrying a Strep-tag and RocG expression was induced by arginine (PubMed). Expression of the Strep-tagged GltC protein allows to test the functionality of the protein. Crude extracts (10-15 ml) were prepared by using a French Press. After a centrifugation step for 1 h @ 27.000 g the clarified crude extracts were loaded onto a Streptactin sepharose column (0.5-1 ml matrix) to isolate the cross-linked protein complexes (the detailed procedure for protein purification is described in the IBA manual, http://www.iba-go.com/). After the purification of the protein complexes the crosslinks can be resolved by boiling the samples in Laemmli buffer for 10-15 minutes @ 95 °C (PubMed). A 12.5% SDS gel was loaded with the samples and the proteins were then visualized by silver-staining. The interaction partner/s were identified by mass spectroscopy and Western blotting.

Preparation of the formaldehyde stock solution (max. 4% in 1 X PBS pH 6.5): We use para-formaldehyde (a white powder; http://en.wikipedia.org/wiki/Paraformaldehyde). para-formaldehyde dissolves within approx. 20-30 minutes in 1 X PBS for @ 65 to 70 °C.

The sepharose matrix was purchased from the IBA company, Göttingen (http://www.iba-go.com/).

Relevant plasmids:

for use in B. subtilis (multicopy plasmids): pGP380, pGP382

for use in B. subtilis (chromosomal integration under the control of the native promoter): pGP1389

for use in E. coli: pGP172, pGP574

Biotin-containing proteins that are purified with the Strep-Tactin column

PycA, AccB