Protein A, G and L are recombinant fusion proteins that combine all immunoglobulin binding regions of Protein A, G and L. Their binding capacity covers all immunoglobulins of host animals commonly used in biomedicine except IgY, including antibody classes such as IgG, IgM, IgA, IgE and IgD, their subclasses, and antibody fragments such as Fab, scFv and sdAb. Thus, Protein A, G, and L have the broadest immunoglobulin (antibody) binding spectrum. For specific immunoglobulin molecules, Protein A, G, and L can produce the highest binding power and maximum binding at multiple sites through synergistic effects. In addition, Protein A, G, and L specifically bind to the surface conformation sites of naturally active immunoglobulins and do not bind to denatured or inactivated immunoglobulins that have lost that natural conformation.
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Protein A expressed from E. coli is functionally close to the natural protein A. It contains 5 IgG antibody binding regions (E-D-A-B-C) that bind to the immunoglobulin Fc fragment and is ideal for purification of monoclonal and polyclonal IgG antibodies.
Protein G is a cell wall protein isolated from Streptococcus haemolyticus with high affinity for the Fc segment of immunoglobulins of the same type or different subtypes of different species. The genetically engineered protein G contains three immunoglobulin binding regions and is able to bind IgG from human, mouse, rat, guinea pig, rabbit, goat, sheep and horse. Moreover, it can also bind Fab segment, which facilitates the purification of Fab segment of IgG.
The recombinant genetically engineered protein A/G contains five immunoglobulin binding regions of Protein A and two binding regions of Protein G. The binding capacity is greatly improved compared to that of single Protein A and Protein G. The enhanced binding capacity of the Fc segment makes it a more popular tool for immunoglobulin purification. Protein A/G binds all human IgG isoforms as well as IgA, IgE, IgM and to a lesser extent IgD.
Protein L contains five kappa-binding regions that bind to the immunoglobulin κ light chain without affecting antigen binding, and has a broader range of Ig and Ig isoforms than other antibody-binding proteins.
Protein A/G/L contains 5 antibody binding regions of Protein L, 5 antibody binding regions of Protein A and 2 antibody binding regions of Protein G. Binds all human IgG subtypes and IgA, IgE, IgM and IgD.