title: Protein L from Peptostreptococcus magnus binds to the kappa light chain variable domain.
abstract: Protein L is an immunoglobulin light chain-binding protein expressed by some strains of the anaerobic bacterial species Peptostreptococcus magnus. The major variable region subgroups of human kappa and lambda light chains were tested for protein L binding; V kappa I, V kappa III, and V kappa IV bound protein L, whereas no binding occurred with proteins of the V kappa II subgroup or with any lambda light chain subgroups. Studies of the protein L binding capacity of naturally occurring VL fragments, and VL- and CL-related trypsin- and pepsin-derived peptides prepared from a kappa I light chain, localized the site of interaction to the VL domain. The affinity constant for the binding to an isolated V kappa I fragment was comparable to that for the native protein (Ka 0.9 x 10(9) M-1 and Ka 1.5 x 10(9) M-1, respectively). No binding occurred with CL-related fragments. Extensive reduction and alkylation of the V kappa fragment or the native kappa chain resulted in complete loss of protein L binding. Although it is possible, from comparative amino acid sequence data, to identify certain VL-framework region residues that account for the selective binding of protein L by kappa I, kappa III, and kappa IV proteins, our studies indicate that this interaction is essentially dependent upon the tertiary structural integrity of the kappa chain VL domain.
authors.affiliation: Department of Medical and Physiological Chemistry, University of Lund, Sweden.
authors.forename: B H
authors.initials: BH
authors.lastname: Nilson
authors.forename: A
authors.initials: A
authors.lastname: Solomon
authors.forename: L
authors.initials: L
authors.lastname: Björck
authors.forename: B
authors.initials: B
authors.lastname: Akerström
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000378:metabolism*; D002853:Chromatography, Liquid; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007135:Immunoglobulin Variable Region; D007145:Immunoglobulin kappa-Chains / Q000378:metabolism*; D008969:Molecular Sequence Data; D010434:Pepsin A / Q000378:metabolism; D010462:Peptostreptococcus / Q000378:metabolism*; D011487:Protein Conformation; D011863:Radioimmunoassay; D014357:Trypsin / Q000378:metabolism; D014961:X-Ray Diffraction
chemical_list: D001426:Bacterial Proteins; C055047:Ig L-binding protein, Peptostreptococcus; D007135:Immunoglobulin Variable Region; D007145:Immunoglobulin kappa-Chains; D014357:Trypsin; D010434:Pepsin A