Protein Purification

Chondrex, Inc. offers a range of resins for protein purification. The following provides more information on different protein purification mechanism in order to help you  choose the appropriate resins for your research and purposes.

Protein Purification Resins

1. Ion-exchange Chromatography (1, 2)

Each protein has a net charge, called isoelectric point (pI),  determined by its primary amino acid sequences.  When the pH of the buffer surrounding the protein equals its pI, the protein carries no net charge. At a pH below the pI, the protein carries a net positive charge, while , at a pH higher than the pI, the protein carries a net negative charge.

This charge property allows proteins to selectively bind to resins with opposite charges in ion-exchange chromatography. This technique utilizes the following principal - positively charged resins (anion exchange: DEAE and Q), or negatively charged resins (cation exchange: CM ). At a particular buffer pH, all appropriately charged proteins will bind to the resin. Then, alterations in pH or salt gradients facilitate the elution of proteins from the resin.

For example, at a pH of 7.5, proteins with a pI above 7.5 will bind to a cation exchange resin due to their net positive charge, while those with a pI below 7.5 will bind to an anion exchange resin. The pI values of commonly used proteins are BSA: 5.1-5.5, OVA: 5.2, and human IgG: 6.6-7.2.

2. Affinity Chromatography (3)

Affinity chromatography is a highly effective method for the purification of specific proteins through biological interactions, leveraging strong yet reversible binding between molecules like receptor-ligand or antibody-antigen. This method immobilizes one of the interacting proteins on a chromatographic resin, allowing for the selective binding and subsequent elution of the target protein by altering conditions, such as  pH or salt concentration.

Proteins A and G, derived from Staphylococcus aureus and Streptococcus species, respectively, have been used to purify IgG due to their immunoglobulin-binding properties. Based on the target protein stability, the purification procedures must  be optimized by choosing elution conditions such as lowering pH or using potassium thiocyanate (KSCN), a chaotropic agent that disrupts the molecular interactions. These conditions release IgG from the resin conjugated with protein A or G (4, 5).

The incorporation of poly histidine (His) residues (generally six His) into proteins facilitates their binding to immobilized metal ions, such as nickel (Ni) under defined conditions. This unique interaction establishes an affinity chromatography purification method between Ni-Nitrilotriacetic acid (NTA) coupled resin and His-tagged proteins. The procedure accommodates both native conditions and denaturing conditions containing a chaotropic reagent such as urea or guanidine hydrochloride to unfold the protein, thereby solubilizing proteins and exposing the His-tags for effective binding. His-tagged proteins can be effectively eluted from the resin by adjusting the concentration of imidazole, which competes with the His residues for binding sites on the metal ions, or by altering the pH, which affects the charge interactions between the protein and the immobilized metal ion (6).

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Produce List

Note: Affinity of Protein A/G for Immunoglobulin Types from Different Species

Protein A and Protein G exhibit specific binding affinities for various immunoglobulin (Ig) subtypes, subclasses, and species, which are determined by the characteristics of the Ig Fc region. The details of their binding affinities are listed in the following chart that categorizes the interaction strengths of Protein A and G with immunoglobulin subclasses across different species.

References

1.     P. M. Cummins, K. D. Rochfort, B. F. O’Connor, Ion-Exchange Chromatography: Basic Principles and Application. Methods Mol. Biol. 1485, 209–223 (2017).

2.     A. Jungbauer, R. Hahn, “Chapter 22 Ion-Exchange Chromatography” in Methods in Enzymology, R. R. Burgess, Deutscher, Murray P., Eds. (Academic Press, 2009)vol. 463, pp. 349–371.

3.     M. Urh, D. Simpson, K. Zhao, Affinity chromatography: general methods. Methods Enzymol. 463, 417–438 (2009).

4.     W. Choe, T. A. Durgannavar, S. J. Chung, Fc-Binding Ligands of Immunoglobulin G: An Overview of High Affinity Proteins and Peptides. Materials  9 (2016).

5.     J. B. Fishman, E. A. Berg, Protein A and Protein G Purification of Antibodies. Cold Spring Harb. Protoc. 2019 (2019).

6.     A. Spriestersbach, J. Kubicek, F. Schäfer, H. Block, B. Maertens, Purification of His-Tagged Proteins. Methods Enzymol. 559, 1–15 (2015).

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