Recovery of polypeptides from polyacrylamide gels by electrophoretic elution in a centrifugation concentrator

Preparative isolation of protein complexes and other bioparticles by elution from polyacrylamide gels

Due to its unmatched resolution, gel electrophoresis is an indispensable tool for the analysis of diverse biomolecules. By adaptation of the electrophoretic conditions, even fragile protein complexes as parts of intracellular networks migrate through the gel matrix under sustainment of their integrity. If the thickness of such native gels is significantly increased compared to the analytical version, also high sample loads can be processed. However, the cage-like network obstructs an in-depth analysis for deciphering structure and function of protein complexes and other species. Consequently, the biomolecules have to be removed from the gel matrix into solution. Several approaches summarized in this review tackle this problem. While passive elution relies on diffusion processes, electroelution employs an electric field to force biomolecules out of the gel. An alternative procedure requires a special electrophoresis setup, the continuous elution device. In this apparatus, molecules migrate in the electric field until they leave the gel and were collected in a buffer stream. Successful isolation of diverse protein complexes like photosystems, ATP-dependent enzymes or active respiratory supercomplexes and some other bioparticles demonstrates the versatility of preparative electrophoresis. After liberating particles out of the gel cage, numerous applications are feasible. They include elucidation of the individual components up to high resolution structures of protein complexes. Therefore, preparative electrophoresis can complement standard purification methods and is in some cases superior to them.

Cloning and analysis of the genes for a novel electron-transferring flavoprotein from Megasphaera elsdenii. Expression and characterization of the recombinant protein

The genes that encode the two different subunits of the novel electron-transferring flavoprotein (ETF) from Megasphaera elsdenii were identified by screening a partial genomic DNA library with a probe that was generated by amplification of genomic sequences using the polymerase chain reaction. The cloned genes are arranged in tandem with the coding sequence for the beta-subunit in the position 5' to the alpha-subunit coding sequence. Amino acid sequence analysis of the two subunits revealed that there are two possible dinucleotide-binding sites on the alpha-subunit and one on the beta-subunit. Comparison of M. elsdenii ETF amino acid sequence to other ETFs and ETF-like proteins indicates that while homology occurs with the mitochondrial ETF and bacterial ETFs, the greatest similarity is with the putative ETFs from clostridia and with fixAB gene products from nitrogen-fixing bacteria. The recombinant ETF was isolated from extracts of Escherichia coli. It is a heterodimer with subunits identical in size to the native protein. The isolated enzyme contains approximately 1 mol of FAD, but like the native protein it binds additional flavin to give a total of about 2 mol of FAD/dimer. It serves as an electron donor to butyryl-CoA dehydrogenase, and it also has NADH dehydrogenase activity.

Electrophoretic elution of macromolecules from polyacrylamide or agarose gels

A method for elution of micrograms of macromolecules from polyacrylamide and agarose gels is described. The recoveries were greater than 90% with three different macromolecules tested (28 to 360 kDa). An amount as small as 1 microgram of human serum albumin was eluted from polyacrylamide gel with 90% recovery. The eluted material is collected into a small chamber the size of which can be changed as required. Elution and concentration are achieved simultaneously and in one step under mild conditions. Sterile eluates can be obtained, if the apparatus is constructed under sterile conditions.

Homogeneous preparation of human thymidine-5'-triphosphatase by electroelution from SDS/PAGE with subsequent renaturation

This paper describes a rapid and inexpensive method for homogeneous enzyme preparation from SDS/polyacrylamide gels with subsequent renaturation. The method was optimized for an enzyme of pyrimidine metabolism, thymidine-5'-triphosphatase (dTTPase), present in human serum in small amounts. After gel electrophoresis, the enzyme was eluted from gel pieces in an elution chamber based on a tube gel electrophoresis system. Renaturation conditions were optimized in preliminary tests. The best results were obtained with an initial acetone precipitation to remove sodium dodecyl sulfate. The precipitate was then dissolved in 8 M guanidine hydrochloride and diluted 50-fold for renaturation. Adding 1.5 mg/ml lauryl maltoside to the renaturation buffer, followed by subsequent dialysis of the renaturating samples, improved the renaturation yield up to 95%. This method was used to purify dTTPase to homogeneity from a partially purified sample, and to determine the molecular mass of the subunits. The procedure can also be applied to other enzymes and could give rise to a general strategy for enzyme purification.

Sequential sodium dodecyl sulfate-polyacrylamide gel electrophoresis and reversed-phase chromatography of unfolded proteins

Sequential sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis and reversed-phase high performance liquid chromatography on a fluorocarbon packing (poly F column, DuPont) provide fully denatured but highly purified protein, which is free of low-molecular-weight substances and directly amenable to structural analysis. Conditions for the preparative elution of four test proteins (bovine serum albumin, carbonic anhydrase, myoglobin, cytochrome c) blotted to Immobilon membranes have been optimized. Phenol saturated with 50 mM Tris-HCl (pH 8.25) and containing 2% SDS and 1% 2-mercaptoethanol is able to elute proteins that have been blotted to Immobilon membranes, stained with Coomassie R-250, and stored as dry sheets, largely irrespective of their molecular mass. Polypeptides that are not degraded by exposure to low pH can also be efficiently extracted directly from stained gels with 70% formic acid. If further separation of polypeptides is not needed, a simple run of a protein sample dissolved in 1-2% SDS on the poly F column will efficiently remove low-molecular-weight substances, including SDS.

Ultraviolet scanning densitometry for detection, quantitation, and preparative elution of protein bands from unstained gels

Ultraviolet scanning of gel rods was used to identify and quantify protein bands in a nondestructive manner with good precision and sensitivity. This same technique, applied on a preparative scale, allowed quantitative protein elution, by reversed electrophoresis, from gel slices completely sealed in a dialysis bag. Protein recovery approached the theoretical yield (93.5 +/- 5%), with practically no interfering substances, and the entire preparative process (first electrophoresis, densitometric scanning, and reversed electrophoresis) could be performed in approximately 6 h. Its application to human growth hormone has shown no alteration in the biological activity of this protein.

Removal of dodecyl sulfate from protein solution

Sodium dodecyl sulfate is one of the most widely used detergents. But, there is no good method to remove dodecyl sulfate (DS) from a small volume of protein solution. We showed that (a) DS in protein solution was removed by the addition of potassium salts with high recovery of protein, and (b) the method was useful before tryptic digestion of protein.