Efficient Purification of Elastin-Like Polypeptides (ELPs) from E. coli Using an Organic Solvent-based Extraction and Precipitation Method

Summary

This protocol describes a rapid, reproducible organic solvent-based extraction and precipitation method for purifying elastin-like polypeptide (ELP) from Escherichia coli, providing a potentially scalable alternative to conventional ELP purification methods.

Abstract

Elastin-like polypeptides (ELP) are engineered biopolymers built from repetitive pentapeptide sequences that mimic motifs found in mammalian tropoelastin. Their unique characteristics make them ideal candidates for a wide array of biomedical applications, ranging from drug and gene delivery to tissue engineering and targeted molecular imaging. Conventional purification approaches from Escherichia coli (E. coli) expression can be ineffective for ELP due to the formation of inclusion bodies. Other methods, such as inverse transition cycling (ITC), utilize the lower critical solution temperature (LCST) properties of ELP to separate it from contaminants such as lipopolysaccharides (LPS), but typically require multiple heating and cooling steps that are time-consuming and can result in low recoveries depending on the sequence, concentration, and molecular weight of the ELP construct. To tackle these challenges, we have developed an organic solvent-based extraction-precipitation workflow that exploits the intrinsic hydrophobicity of ELP to enable rapid, robust, and broadly applicable purification directly from E. coli cell pellets. This method uses polar organic solvents to aid in cell disruption and selectively solubilize ELP in a single step. A subsequent precipitation step effectively removes residual organic solvents, low-molecular-weight impurities, and endotoxins, yielding highly pure ELP with LPS levels below 1 EU/mL in under 3 h. Atomic force microscopy data suggest that ELP-fusion proteins purified in this manner can self-assemble into reverse micelle-like structures that retain fusion protein function. This rapid purification method offers researchers a straightforward and potentially scalable way to purify ELP, creating new possibilities for using ELP and their fusion proteins as flexible building blocks for material and biomedical applications.

Introduction

Elastin-like polypeptides (ELPs) are biopolymers composed of repeating (VPGXG)n motifs^{1,2,3,4,5,6,7,8,9}. The guest residue X in the pentapeptide unit can be any amino acid other than proline. Variations in X can be used to tune the hydrophobicity, thermal transition behavior, and functional characteristics of the ELP construct to create modular biocompatible materials t....

Protocol

1. Materials preparation

1. Bacterial strain: Use Escherichia coli BL21(DE3) chemically competent cells as the expression host.
   NOTE: They were selected due to their high transformation efficiency and suitability for recombinant protein production.
2. Expression plasmid: Use pET21(+) vector encoding ELP-I-Cm2 fusion protein with ampicillin-resistance⁹. Purchase the plasmid vector from addgene. Insert the Cm2 gene using the BsrG I site at the end of the intein.
   NOTE: The plasmid DNA sequence for this protein is provided in Supplementary File 1.
3. Growth media: Terri....

Results

After going through the final phases of the protocol, the next step is visualization of the extraction-precipitation outcome by SDS-PAGE analysis and Coomassie blue staining. When there is a lysis step prior to organic extraction, a prominent ELP band should be apparent. In the case of ELP-I-Cm2, this band appears at 100 kDa (Figure 3A).

Screening of different organic solvent combinations demonstrated variable extraction efficiencies (Figure 3.......

Discussion

ITC has previously been used for non-chromatographic purification of ELP¹⁹; however, it can be a time-consuming method and low-yielding process. In the methods detailed above, we describe an approach for the rapid purification of an ELP-I-Cm2 fusion protein, demonstrating how the organic solvent-based extraction-precipitation method can be effectively used for the purification of a wide variety of ELP and ELP fusions. The organic solvent protocol is not only faster than ITC, but also much more eff.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
2-Mercaptoethanol	Bio-Rad	161-0710	SDS-PAGE Component
30% Acrylamide/Bis-acrylamide	TCI	A3218	SDS-PAGE Component
Acetone	Fisher Scientific	A949	Organic Solvent
Acetonitrile	Fisher Scientific	A996	Organic Solvent
Ampicilin	Gold Bio- Gold Biotechnology	A-301-25	Antibiotic
APS (Ammonium Persulfate)	Bio-Rad	1610700	SDS-PAGE Component
Butanol	Fisher Scientific	L13171	Organic Solvent
EDTA	Fisher Bioreagents	BP118-500	Lysis Buffer Component
Ethanol	Decon Labs	UN1170	Organic Solvent
Ethyl Acetate	Fisher Scientific	E195	Organic Solvent
Glycerol	Research Products International	G22020-0.5	Terrific Broth (TB) Media Component
Hydrochloric Acid	Fisher Scientific	A144SI-212	Lysis Buffer Component
Instant Coomasie stain	Abcam	ab119211	SDS-PAGE Component
IPTG	Gold Bio- Gold Biotechnology	12481C25	Protein Expression Component
Isopropanol	Fisher Scientific	A451-1	Organic Solvent
K2HPO4 (Potassium Phosphate Monobasic)	Wards' Science	470302-246	Part 2 Buffer Component
KH2PO4 (Potasium Phosphate Dibasic)	Wards' Science	470302-254	Part 2 Buffer Component
L-Proline	Research Products International	P5200-500.0	Terrific Broth (TB) Media Component
Lysozyme	Gold Bio- Gold Biotechnology	L-040-1	Lysis Buffer Component
Methanol	Fisher Scientific	A452	Organic Solvent
Native Sample Buffer	Bio-Rad	161-0738	SDS-PAGE Component
Protein Ladder	Gold Bio- Gold Biotechnology	P008-500	SDS-PAGE Component
Resolving Gel Buffer	Bio-Rad	1610798	SDS-PAGE Component
Sodim Dodecyl Sulfate (SDS)	Thermo Scientific	J18220-36	SDS-PAGE Component
Sodium Hydroxide	Fisher Scientific	S318-500	Lysis Buffer Component
Stacking Gel Buffer	Bio-Rad	1610799	SDS-PAGE Component
TEMED	Bio-Rad	1610801	SDS-PAGE Component
Tris Base	Fisher Bioreagents	BP-152	Lysis Buffer Component
Tryptone	Research Products International	T60065-1000.0	Terrific Broth (TB) Media Component
Yeast Extract	Research Products International	Y20025-1000.0	Terrific Broth (TB) Media Component