Recovery of protein from sodium dodecyl sulfate--polyacrylamide gels

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.

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.

Purification of membrane proteins in SDS and subsequent renaturation

A prerequisite for the purification of any protein to homogeneity is that the protein is not non-specifically associated with other proteins especially during the final stage(s) of the fractionation procedure. This requirement is not so often fulfilled when nonionic detergents (for instance Triton X-100) are used for solubilization of membrane proteins. The reason is that these detergents are not efficient enough to prevent the protein of interest from forming aggregates with other proteins upon contact with chromatographic or electrophoretic supporting media, which, due to their polymeric nature, have a tendency to induce aggregation of other polymers, for instance, hydrophobic proteins. The aggregation can be avoided if sodium dodecyl sulfate (SDS) is employed as detergent. We therefore suggest that membrane proteins should be purified by conventional methods in the presence of SDS and that the purified proteins, which are in a denatured state, are allowed to renature. There is good change to renature internal membrane proteins since they should not be so susceptible to denaturation by detergents as are water-soluble proteins because the natural milieu of the former proteins is lipids which in fact are detergents. In this paper we present a renaturation method based on the removal of SDS by addition of a large excess of G 3707, a nonionic detergent. By this technique we have renatured a 5'-nucleotidase from Acholeplasma laidlawii and a neuraminidase from influenza virus. The enzyme activities were higher (up to 6-fold) after the removal of SDS than prior to the addition of SDS.

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

A method for recovery of polypeptides from polyacrylamide gels by electrophoretic elution in a commercially available concentrator, the Amicon-Centricon sample reservoir, has been devised. The recoveries were greater than 90% with four different polypeptides tested (12.5 to 80 kDa). After elution, sample concentration or salt exchange can be carried out without sample transfer. There were no loss of sample during the postelution procedures when the elution buffer was replaced by 0.01 or 0.05% sodium dodecyl sulfate.

Electrophoretic elution of proteins from polyacrylamide gel slices

A method for electrophoretic elution of proteins from polyacrylamide gel slices is described. Eluted proteins were retained by a discontinuous conductivity gradient (M. Otto and M. Snejdárková, Anal. Biochem. 111, 111-114 (1981)). The method has been adapted to slices from slab gels and gels that have been stained and destained. Proteins were eluted as their sodium dodecyl sulfate complexes. Minute amounts of proteins (0.1 microgram) were recovered in high yield (85-95%) in 2 h in less than 0.1 ml volume.