Protein extraction from solid tissue.

Maximal extraction and solubilization of protein from diseased or healthy tissue is important to make the whole protein complement available for proteomic analysis. It also helps to maximize reproducibility and to minimize waste. Minimal degradation of the protein amino acid backbone or dephosphorylation is essential to preserve the analytical utility of the extract. Containment of the sample is important to minimize the risk of contamination to and from the sample. The proposed standard protocol for protein extraction and solubilization can result in 98% solubilization of brain tissue, corresponding to about 100 μg protein per mg tissue wet weight, by a frozen disintegration/SDS-based solubilization method: Tissue is crushed in the frozen state in a cryotube by shaking with a sterile steel ball. The crushing is followed by the extraction and solubilization in 2% SDS for 10 min, at 70°C, in a volume corresponding to ten times the tissue wet weight, with shaking. The containment in a cryotube helps to prevent contamination. The treatment with SDS sample buffer can inhibit protease and phosphatase activity. The resulting protein extracts can be used for SDS PAGE, 2-D PAGE, Western blotting, ESI-MS, and ELISA. The proposed standard protocol has the potential to find wide application where protein extraction, solubilization, identification, and quantitation from cryopreserved clinical samples are desirable.