Highlights:

• Protein L is an immunoglobulin-binding protein that was originally derived from the bacteria Peptostreptococcus magnus, but is now produced recombinantly.^1,2 
• Protein L has the unique ability to bind through kappa light chain interactions without interfering with an antibody's antigen-binding site.³ This gives Protein L the ability to a wider range of Ig classes and subclasses than other antibody-binding proteins (Table 1). Protein L will bind to all classes of Ig (IgG, IgM, IgA, IgE and IgD). Protein L will also bind Single Chain Variable Fragments (ScFv) and Fab Fragments.^3,4 Protein L binds kappa I, III, and IV in human and kappa I on mouse. Furthermore, Protein L has a reported isoelectric point of 4.5.⁵ However, an isoelectric point of 4.8 was obtained by scientists at Pierce Biotechnology, Inc. (unpublished results).

References:

1. Bjorck, L. (1988). Protein L: A novel bacterial cell wall protein with affinity for Ig L chains. J. Immunol. 140(4), 1194-1197.
2. Kastern, W., Sjobring, U. and Bjorck, L. (1992). Structure of peptostreptococcal protein L and identification of a repeated immunoglobulin light chain-binding domain. J. Biol. Chem. 267(18), 12820-5.
3. Nilson, B.H., Logdberg L., Kastern, W., Bjorck L. and Akerstrom, B. (1993). Purification of antibodies using protein L binding framework structures in the light chain variable domain. J. Immunol. Methods 164(1), 33-40.
4. Bottomley, S.P., Beckingham, J.A., Murphy, J.P., Atkinson, M., Atkinson, T., Hinton, R.J. and Gore , M.G. (1995). Cloning, expression and purification of Ppl-1, a kappa-chain binding protein, based upon protein L from Peptostreptococcus magnus. Bioseparation 5(6), 359-67.
5. Murphy, J.P., Atkinson M., Trowern, A.R., Stevens, G.B., Atkinson, T., Duggleby, C.J. and Hinton, R.J. (1996). Amplified expression and large-scale purification of protein L. Bioseparation 6(2), 107-13.