Protein L is different from protein A and protein G—Protein L binds predominantly to kappa light chains, without interfering with the antigen-binding site. Its interaction with Ig from various species varies. Protein L reacts strongly with human, baboon, guinea pig, mouse, rat, and pig IgG, and weakly with rabbit, horse, and goat IgG.

It may be used for the purification of IgG, IgM, IgA, IgE and IgD containing kappa light chains and for the purification of Fab and scFv fragments containing kappa light chains. It may be conjugated to a solid support for affinity purification or to marker molecules for detection. Protein L does not bind to bovine, sheep, or goat immunoglobulins.

Application:
Protein L has potential as a universal Ig ligand due to its interaction with the light chain. Its unique ability to bind kappa light chains makes it valuable in detection and purification of antibodies and antibody fragments.