Mapping of the immunoglobulin light chain-binding site of protein L

M. Wikström (Corresponding Author), U. Sjöbring, Sture Forsen, Torbjörn Drakenberg, L Björck

Research output: Contribution to journalArticleScientificpeer-review

43 Citations (Scopus)


Protein L is a cell surface protein expressed by some strains of the anaerobic bacterial species Peptostreptococcus magnus. The molecule binds specifically and with high affinity to immunoglobulins (Ig) of a wide range of animal species.
The Ig-binding activity is mediated through five highly homologous domains, each 72 to 76 amino acid residues long, which interact with framework regions in the variable domain of Ig light chains. The interaction does not interfere with the antigen binding capacity of the antibody.
The fold of the Ig light chain-binding domains of Protein L is comprised of an α-helix packed against a four stranded β-sheet and is similar to the fold of the IgG heavy chain-binding domains of streptococcal protein G, despite the fact that the two proteins show no significant sequence homology. In the present work, heteronuclear NMR spectroscopy has been utilized to define the interaction between the N-terminal Ig-binding domain of Protein L and the variable domain of a human Ig kappa light chain.
The Ig-binding region of the Protein L domain involves most of the residues in the second β-strand, the C-terminal residues of the α-helix and the loop connecting the α-helix with the third β-strand. The Ig light chain-binding surface of Protein L thus resembles the surface of Protein G which binds to the Cγ1 domain of IgG, but is different from the portion of Protein G involved in the contact with the Cγ2–Cγ3 interface region.
The data suggest that the global fold shared by the Ig-binding domains of Proteins L and G provide bacteria with a flexible template for the evolution of surface structures capable of interacting with different conserved parts of Ig molecules of the infected host
Original languageEnglish
Pages (from-to)128-133
JournalJournal of Molecular Biology
Issue number2
Publication statusPublished - 1995
MoE publication typeA1 Journal article-refereed

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