IgA Purification

Peptide M is a 50 aa synthetic peptide derived from a streptococcal M protein containing an additional C-terminal cysteine residue.
Peptide M binds monomeric and dimeric human IgA of both subclasses (IgA1 and IgA2) with high specificity and affinity. It also binds bovine IgA but not murine IgA.
Peptide M binding occurs at a site in IgA-Fc conserved in human IgA1 and IgA2 and bovine IgA but not in mouse IgA. Peptide M can be used for single-step affinity purification of IgA and for specific detection of antigen-bound IgA.

Sandin C. et al., 2002. Isolation and detection of human IgA using a streptococcal IgA binding peptide. J Immunol. 169(3):1357-64.

SSL7 (Staphylococcus aureus superantigen-like protein 7; formally known as SET1), is a staphylococcus toxin isolated from Staphylococcus aureus. SSL7 binds with a high affinity to the monomeric form of human IgA1 and IgA2. SSL7 has no affinity for human IgG, therefore, it can be used to purify human IgA from human sera, milk and other biological samples [1,2]. SSL7 also binds the secretory form of IgA found in milk from humans, cows, and sheep. SSL7 will bind bovine IgA antibodies present in milk, but not bovine IgA present in serum. SSL7 does not bind mouse, rabbit, sheep or goat IgA present in serum [1].

1. Langley et al., 2005. The staphylococcal superantigen-like protein 7 binds IgA and complement C5 and inhibits IgA-Fc alpha RI binding and serum killing of bacteria. J Immunol 174 :2926-2933.
2. Ramsland PA. et al., 2007. Structural basis for evasion of IgA immunity by Staphylococcus aureus revealed in the complex of SSL7 with Fc of human IgA1. PNAS 104:15051-15056.

Jacalin is an a D-galactose binding lectin extracted from jack-fruit seeds (Artocarpus integrifolia). Jacalin immobilized on supports such as agarose is useful for the purification of human serum or secretory IgA1 [1,2]. IgA can be separated from human IgG and IgM in human serum or colostrums using immobilized Jacalin.
This support is also useful for removing contaminating IgA from IgG samples. Additionally, Jacalin binds IgD [1]. Jacalin can also be used to separate IgA1 subclass from IgA2 [2]. Care needs to be taken when purifying antibodies produced in the presence of bovine serum as Jacalin will bind bovine glycoproteins, such as fetuin, which may interfere with the purity of the eluted antibody.

1. Aucouturier P. et al., 1998. Jacalin, the human IgA1 and IgD precipitating lectin, also binds IgA2 of both allotypes. J Immnuol Methods 113:185-191.
2. Gregory RL. et al., 1987. Separation of human IgA1 and IgA2 using jacalin-agarose chromatography. J Immunol Meth 99:101-106.

Protein L is an immunoglobulin-binding protein expressed by the anaerobic bacterial species Peptostreptococcus magnus [1]. Protein L binds specifically to the variable domain of Ig κ light chain, as a consequence Protein L has the capacity to purifiy κ light containing IgA antibodies [2]. It binds strongly to human κ light chain subclasses I, III and IV, and also to most κ light chains of other species such as rat and mouse. As it recognizes κ light chains, protein L can bind to all classes of Ig, in contrast to Protein A and Protein G which interact with the Fc region and bind exclusively to IgG heavy chains. Protein L does not bind bovine immunoglobulins which are present in the fetal bovine serum (FBS) and thus provides a convenient way to purify κ light chain-containing monoclonal antibodies from culture supernatant.

1. Björck L., 1988. Protein L. A novel bacterial cell wall protein with affinity for Ig L chains. J Immunol. 1988 Feb 15;140(4): 1194-7.
2. Nilson BH. et al., 1993. Purification of antibodies using protein L-binding framework structures in the light chain variable domain. J Immunol Methods. 164(1):33-40.

Protein G is an immunoglobulin-binding protein expressed in group C and G Streptococcal bacteria. It is a 65-kDa (G148 protein G) and a 58 kDa (C40 protein G) cell surface protein that has found application in purifying antibodies through its binding to the Fc region [1].
Protein G binds to most mammalian IgGs through the Fc region, but some binding also occurs through the Fab region.
Native protein G also binds albumin, however, because serum albumin is a major contaminant of antibody sources, the albumin binding site has been removed from recombinant forms of Protein G [2].
Protein G / Agarose from InvivoGen uses the recombinant form of protein G lacking the albumin-binding region.
In Protein G / Agarose, the recombinant protein G is coupled to beads using a leak-resistant chemistry that provides a support with minimal non-specific binding.

1. Sjobring U. et al., 1991. Streptococcal Protein G. Gene structure and protein binding properties. J Biol Chem. 140:1194-1197.
2. Goward CR. et al., 1990. Expression and purification of truncated recombinant streptococccal Protein G. Biochem J. 267:171-177.