Quantitative determination of proteins from formalin-fixed tissue
The invention relates to a method with which proteins from formalin-fixed biological samples can be dissolved and subsequently quantified. The method makes it possible to extract intact full-length proteins from the samples and to conduct a subsequent analysis thereof.
1. A method for the extraction of proteins from a formalin-fixed biological sample, comprising incubating the formalin-fixed biological sample in a buffer at a temperature that is sufficient to release the proteins, wherein the buffer comprises a detergent and no proteolytically active compound, and the biological sample in the buffer is first boiled and then incubated further at a temperature greater than 80° C. but is not further boiled.
2. The method according to claim 1 , wherein the biological sample is boiled in the buffer for 5 to 40 minutes.
3. The method according to claim 1 , wherein the biological sample is incubated at a temperature above 80° C. for a period of 20 minutes to 16 hours.
4. The method according to claim 1 , wherein the released proteins are intact.
5. The method according to claim 1 , wherein the detergent is sodium dodecyl sulphate (SDS), sodium deoxycholate, 3-((3-Cholamidopropyl)dimethylaminonio)-1-Propanesulfonic Acid (CHAPS), a non-ionic surfactant having a hydrophilic polyethylene oxide group and a hydrocarbon lipophilic or hydrophobic group (Triton X100), a non-ionic, non-denaturing detergent having an alkenylphenoxypolyethoxide group and an alcohol group (Nonidet P40) or polysorbate-20 (Tween20).
6. The method according to claim 1 , wherein the buffer additionally comprises at least one reducing agent selected from the group consisting of 1,4-dithio-DL-threitol, dithioerythritol (DTE), tris (2-carboxyethyl)phosphine (TCEP) or monoethanolamine (MEA).
7. The method according to claim 1 , wherein the biological sample, when it is a formalin-fixed sample embedded in paraffin, is deparaffinated before the protein extraction.
8. The method according to claim 1 , wherein after extraction the proteins are further fractionated.
9. The method according to claim 1 , wherein the extracted proteins are subsequently quantified.
10. The method according to claim 1 , wherein the extracted proteins are treated with at least one proteolytic enzyme selected from the group consisting of trypsin, chymotrypsin, proteinase K, papain, pepsin, pronase, endoproteinase Lys-C, and endoproteinase glu-C or at least one glycosidase selected from the group consisting of endoglycosidase H, N-glycosidase F, neuroaminidase and phosphatases.
11. The method according to claim 1 , wherein the proteins are used for at least one biochemical assay.
12. The method according to claim 1 , wherein the biological sample is a tissue sample.
13. The method according to claim 1 , wherein the proteolytically active compound is a protease.
14. The method according to claim 1 , wherein the sample is incubated at a temperature above 80° C. for more than 50 seconds.
15. The method according to 8 , wherein the extracted proteins are fractionated with one or several method stages.
16. The method according to claim 9 , wherein the quantification of the proteins is carried out by the method of Lowry or the bicinchoninic acid (BCA) method.
17. The method according to claim 11 , wherein the biochemical assay is a protein array.
18. The method according to claim 11 , wherein the biochemical assay is used to identify one or more diagnostically or clinically relevant marker proteins present in the biological sample.
19. The method according to claim 17 , wherein the protein array is a sandwich immunoarray, an antigen capture array or a direct protein array.
20. The method according to claim 18 , wherein the marker proteins from at least two biological samples are compared with one another.