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Protein A, protein G and protein L

Antibody purification using antibody-binding proteins

Protein A, protein G, and Protein L are native and recombinant proteins of microbial origin that bind to mammalian immunoglobulins (Ig). Protein A and protein G bind with high affinity and specificity to the Fc region of immunoglobulins from various mammalian species, most notably the IgGs. Protein L binds immunoglobulins via the kappa light chain. These antibody-binding proteins can be used to purify, immobilize or detect immunoglobulins. These proteins (i.e. protein A, protein G, protein L) are typically attached onto a solid support such as sepharose or magnetic beads. Table 1 summarizes the various formats available for the antibody-binding proteins.

Table 1. Formats available for antibody-binding proteins

Antibody-binding protein Sepharose beads Magnetic beads Sepharose column
Protein A ABIN412439 ABIN400575 ABIN412448
Protein G ABIN412450 ABIN400576 ABIN412455
Protein L ABIN412460 ABIN412464 ABIN629427
Protein A / G ABIN412443 ABIN400577 ABIN629425
Protein A / G / L ABIN412465 ABIN412469 ABIN629429

Mammalian immunoglobulin (Ig) can be purified from cell culture media, ascites and serum samples. These antibody-protein bound beads offer a convenient method to achieve high purity and high recovery of monoclonal and polyclonal antibodies from various biological samples. Naturally, the binding specificities and affinities of these proteins would vary between source species and antibody subclass. Table 2 summarizes the antibody binding specificities of each antibody-binding protein for human, mouse and rat.


Table 2. Protein A / G / L binding affinities for immunoglobulins

Species Immunoglobulin Protein A Protein G Protein L
H IgG (normal) ++++ ++++ ++++
H IgG1 ++++ ++++ ++++
H IgG2 ++++ ++++ ++++
H IgG3 - ++++ ++++
H IgG4 ++++ ++++ ++++
H IgM - - ++++
H IgA - - ++++
H IgE - - ++++
H IgD - - ++++
H Fab ++ ++ ++++
M IgG1 + ++++ ++++
M IgG2a ++++ ++++ ++++
M IgG2b +++ ++++ ++++
M IgG3 ++ +++ ++++
R IgG1 - + ++++
R IgG2a - ++++ ++++
R IgG2b - ++ ++++
R IgG2c + ++ ++++
Note: H = human, M = mouse, R = rat