Question 1: Can cell lysates be used with this kit as the source of a test protein?
Answer 1: Yes, cell lysates can be used as the source of the test protein for examining binding between tubulin monomers, polymers and the protein of interest. However, Cytoskeleton does not recommend this as the purity and concentration of the protein will often be too low to interact with tubulin monomers and polymers. Also, the lysates will contain additional accessory proteins and multiple phosphatases and proteases that can interfere or alter the interactions between tubulin and the test protein. We recommend consulting these citations which used cell lysates with this kit: Monzo et al., 2005. Clues to CD2-associated protein involvement in cytokinesis. Mol. Biol. Cell. 16, 2891&ndash, 2902, Moshnikova et al., 2008. Interaction of the growth and tumour suppressor NORE1A with microtubules is not required for its growth-suppressive function. BMC Research Notes. 1, 13. We also recommend the following modifications:
Use 4 x 15 cm plates of cells. Wash and scrape cells with a PIPES-based buffer at 4°, C. Use 3 mls of the following buffer: 20 mM PIPES, pH 7.0, 2 mM MgCl2, 1 mM EGTA, 1 mM GTP, 0.5 mM fresh PMSF (a protease inhibitor that has only 30 min half-life in aqueous solutions), and 1:100 dilution of 100X protease inhibitor cocktail (Cat. # PIC02). Collect the scraped cells and lyse the cells with sonication at 4°, C with 5 pulses on medium for 15 secs each with a 1 min cool down in between each sonication burst. Then centrifµ, ge the lysate at 14, 000 x g in a microfµ, ge at 4°, C for 20 min. Measure the protein in the supernatant and proceed by mixing 2 to 5 mg/ml of extract with 0.5 mg/ml microtubules, as described in the kit.
Question 2: What is an appropriate buffer for the test protein?
Answer 2: The test protein must be in an appropriate buffer to allow attachment to microtubules. Conditions which do not favor microtubule binding are: high salt (e.g. >, 50 mM Buffer or NaCl), high or low pH (i.e. pH of <, 6.0 or >, 9.0) and high calcium (greater than 0.1 mM calcium will depolymerize microtubules). EGTA is included at 1mM to chelate excess calcium.
It is often advisable to include 5.0 mM Mg2+ in the buffer. Appropriate buffers include: HEPES, PIPES and MES, all at 20 mM. In some cases, the presence of ATP or GTP in the reaction may prevent MAP/microtubule association (e.g., kinesin or dynamin, respectively).
If you have any questions concerning this product, please contact our Technical Service department at infohoelzel.de