Inclusion-body expression, solubilization, refolding and purification
Materials Required
Principle
Inclusion-body recovery uses insoluble recombinant protein aggregates from E. coli as a starting material; the workflow is cell disruption, inclusion-body isolation/washing, denaturant or mild solubilization, refolding into soluble protein, and final chromatographic purification. The readouts are soluble protein recovery, purity by SDS-PAGE/chromatography, structural recovery by methods such as circular dichroism when used, and biological activity when an assay is available[1][2][3][4].
MCE has not independently verified the accuracy of these methods. They are for reference only.
Experimental Materials
• Use an E. coli expression strain carrying the recombinant construct, lysis buffer, wash buffer, urea or guanidine hydrochloride for solubilization, reducing agents when disulfide reshuffling or reduction is required, and refolding buffer selected empirically for the target protein; published protocols support both strong denaturation and milder solubilization approaches, including alkaline low-urea methods for some proteins[2][3][4][5].
• Use SDS-PAGE protein stain for monitoring expression, insoluble fraction enrichment, solubilization, refolding, and purification; use a protein-specific activity assay only when the target protein has a validated activity readout, such as L-asparaginase activity after refolding[5].
• Use a shaker incubator for bacterial expression, centrifuge for harvesting cells and isolating inclusion bodies, cell-disruption equipment such as sonication or homogenization, chromatography equipment for ion-exchange, gel-filtration, or affinity purification, and analytical instruments for SDS-PAGE, absorbance-based protein quantification, chromatography profiles, and optional structural/activity confirmation[2][5][6].
• Use SDS-PAGE protein stain for monitoring expression, insoluble fraction enrichment, solubilization, refolding, and purification; use a protein-specific activity assay only when the target protein has a validated activity readout, such as L-asparaginase activity after refolding[5].
• Use a shaker incubator for bacterial expression, centrifuge for harvesting cells and isolating inclusion bodies, cell-disruption equipment such as sonication or homogenization, chromatography equipment for ion-exchange, gel-filtration, or affinity purification, and analytical instruments for SDS-PAGE, absorbance-based protein quantification, chromatography profiles, and optional structural/activity confirmation[2][5][6].
Experimental Procedure
• Express the recombinant protein in E. coli, harvest cells, disrupt cells, and separate soluble and insoluble fractions by centrifugation; confirm that the target protein is enriched in the pellet before proceeding with inclusion-body processing[2][5].
• Prepare washed inclusion bodies by repeated resuspension and centrifugation of the pellet to reduce soluble host-cell contaminants before solubilization; washed inclusion bodies can provide a partially purified target-protein source before refolding[1][2][3].
• Solubilize washed inclusion bodies using a literature-supported denaturing condition for the target class: guanidine hydrochloride or urea is commonly used for complete unfolding, while mild alkaline low-urea solubilization has been reported for selected proteins such as growth hormone and L-asparaginase[2][3][4][5].
• Clarify the solubilized sample by centrifugation or filtration before refolding so that insoluble debris and unsolubilized aggregates do not enter the refolding or chromatography step[2][5].
• Refold the solubilized protein by dilution, dialysis, pulsatile dilution, or on-column refolding; the appropriate method is protein-dependent, and reported examples include pulsatile dilution for L-asparaginase and matrix/affinity-column refolding for His-tagged proteins[1][5][7].
• Purify refolded protein using chromatography compatible with the protein and tag design; reported workflows include ion-exchange followed by gel filtration for refolded L-asparaginase and immobilized metal-affinity chromatography with on-column refolding for His-tagged proteins[5][7].
• Track recovery and purity at each stage by collecting samples from total lysate, soluble lysate, insoluble pellet, washed inclusion bodies, solubilized protein, refolded protein, and purified fractions; SDS-PAGE and protein quantification are used to evaluate enrichment, solubilization efficiency, refolding recovery, and final purity[2][5].
• Interpret success by combining solubility, purity, oligomeric state when relevant, and biological activity; for L-asparaginase, recovery of active tetrameric protein after refolding and purification was assessed using chromatography and enzyme activity, while broader studies emphasize that refolding conditions must be optimized separately for each protein[1][5].
• Prepare washed inclusion bodies by repeated resuspension and centrifugation of the pellet to reduce soluble host-cell contaminants before solubilization; washed inclusion bodies can provide a partially purified target-protein source before refolding[1][2][3].
• Solubilize washed inclusion bodies using a literature-supported denaturing condition for the target class: guanidine hydrochloride or urea is commonly used for complete unfolding, while mild alkaline low-urea solubilization has been reported for selected proteins such as growth hormone and L-asparaginase[2][3][4][5].
• Clarify the solubilized sample by centrifugation or filtration before refolding so that insoluble debris and unsolubilized aggregates do not enter the refolding or chromatography step[2][5].
• Refold the solubilized protein by dilution, dialysis, pulsatile dilution, or on-column refolding; the appropriate method is protein-dependent, and reported examples include pulsatile dilution for L-asparaginase and matrix/affinity-column refolding for His-tagged proteins[1][5][7].
• Purify refolded protein using chromatography compatible with the protein and tag design; reported workflows include ion-exchange followed by gel filtration for refolded L-asparaginase and immobilized metal-affinity chromatography with on-column refolding for His-tagged proteins[5][7].
• Track recovery and purity at each stage by collecting samples from total lysate, soluble lysate, insoluble pellet, washed inclusion bodies, solubilized protein, refolded protein, and purified fractions; SDS-PAGE and protein quantification are used to evaluate enrichment, solubilization efficiency, refolding recovery, and final purity[2][5].
• Interpret success by combining solubility, purity, oligomeric state when relevant, and biological activity; for L-asparaginase, recovery of active tetrameric protein after refolding and purification was assessed using chromatography and enzyme activity, while broader studies emphasize that refolding conditions must be optimized separately for each protein[1][5].
Troubleshooting
Problem: Refolded protein precipitates or gives low soluble recovery.
• Possible Cause: Aggregation during refolding.• Literature-supported Solution: Reduce the refolding protein concentration, use gradual denaturant removal or dilution-based refolding, and screen refolding conditions rather than assuming one universal buffer[1][3][4].
Problem: Solubilization is high but recovered bioactive protein is low.
• Possible Cause: Strong denaturation may fully unfold protein and increase aggregation during refolding.• Literature-supported Solution: Test milder solubilization conditions for compatible proteins, because mild solubilization has been reported to preserve native-like structure and improve bioactive recovery in some inclusion-body proteins[3][4][5].
Problem: Purified protein is soluble but inactive.
• Possible Cause: Misfolding, incorrect oligomerization, or incorrect disulfide pairing.• Literature-supported Solution: Add a target-specific activity assay and, where applicable, assess oligomeric state by gel filtration; L-asparaginase refolding required recovery of the active tetrameric form, not only soluble monomeric protein[5].
References:
- [1]. Burgess RR. Refolding solubilized inclusion body proteins. Methods Enzymol. 2009;463:259-282. [Content Brief]
- [2]. Palmer I, et al. Preparation and extraction of insoluble (inclusion-body) proteins from Escherichia coli. Curr Protoc Protein Sci. 2004;Chapter 6:Unit 6.3. [Content Brief]
- [3]. Singh SM, et al. Solubilization and refolding of bacterial inclusion body proteins. J Biosci Bioeng. 2005;99(4):303-310. [Content Brief]
- [4]. Singh A, et al. Protein recovery from inclusion bodies of Escherichia coli using mild solubilization process. Microb Cell Fact. 2015;14:41. [Content Brief]
- [5]. Upadhyay AK, et al. Refolding and purification of recombinant L-asparaginase from inclusion bodies of E. coli into active tetrameric protein. Front Microbiol. 2014;5:486. [Content Brief]
- [6]. Yang Z, Zhang L, Zhang Y, Zhang T, Feng Y, Lu X, et al. Highly efficient production of soluble proteins from insoluble inclusion bodies by a two-step-denaturing and refolding method. PLoS One. 2011;6(7):e22981. [Content Brief]
- [7]. Li M, et al. In vitro protein refolding by chromatographic procedures. Protein Expr Purif. 2007;56(2):286-292. [Content Brief]
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