Protein L is a bacterial protein with immunoglobulin (Ig) light chain-binding properties. It contains a number of homologous b1 repeats towards the N-terminus. These repeats have been found to be responsible for the interaction of protein L with Ig light chains [1].

1: Structure of peptostreptococcal protein L and identification of a repeated immunoglobulin light chain-binding domain. Kastern W, Sjobring U, Bjorck L; J Biol Chem 1992;267:12820-12825. PMID:1618782