A mouse Ig kappa domain of very unusual framework structure loses function when converted to the consensus.
Antibody gene sequences, particularly those of kappa light chains, are very well conserved in the framework region, and the variability is concentrated in the complementarity-determining regions (CDR). We now found that the murine antibody 93-6 (Djavadi-Ohaniance, L., Friguet, B., and Goldberg, M. (1984) Biochemistry 23, 97-104) whose Fab fragment binds the beta-subunit of Escherichia coli tryptophan synthase with high affinity (Kd of 6.7.10(-9) M) has a highly unusual kappa light chain framework, which is crucial for the function of this antibody. It carries an insertion of 8 amino acids in a conserved framework loop that faces the antigen, and its framework region 2 (FR2) which precedes CDR2 is shortened by one amino acid, normally leucine and part of an absolutely conserved beta-bulge preceding CDR2. Removal of the insertion to restore the consensus sequence reduced the binding affinity of 93-6 by a factor 3, while insertion of the missing leucine into FR2 completely abolished binding.
Ge
L
L
Biochemisches Institut, Universität Zürich, Switzerland.
Lupas
A
A
Peraldi-Roux
S
S
Spada
S
S
Plückthun
A
A
D000595:Amino Acid Sequence; D000818:Animals; D000907:Antibodies, Bacterial / Q000235:genetics*; D000937:Antigen-Antibody Reactions / Q000235:genetics*; D016384:Consensus Sequence; D017124:Conserved Sequence; D004926:Escherichia coli / Q000201:enzymology; D007145:Immunoglobulin kappa-Chains / Q000235:genetics*; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D014367:Tryptophan Synthase / Q000276:immunology
D000907:Antibodies, Bacterial; D007145:Immunoglobulin kappa-Chains; D014367:Tryptophan Synthase