kappa Chain joining segments and structural diversity of antibody combining sites.

Abstract

Immunoglobulin K light chains are coded for by at least three distinct gene segments designated variable, joining, and constant. The joining gene codes for the 13 amino acid segment linking the variable and constant regions. This peptide includes the last amino acid (96) in the third complementarity-determining region and thus could introduce structural diversity. We have determined the light chain variable region sequences from three myeloma proteins with P(1,6)galactan-binding specificity, bringing to six the number of light chains sequenced from proteins demonstrating this specificity. Five of these have isoleucine at position 96 and the sixth tryptophan. This substitution appears to be accommodated with no significant change in association constant for a 19(1,6)galactan hapten. Additionally, as many as nine substitutions are found in both light and heavy chain complementarity-determining regions between members of this group-although only minimal variations in hapten binding affinity are observed. The isoleucine found at position 96 in five of the X chains could not be coded for by any of the joining gene nucleotide. sequences previously observed and would require a novel nucleotide sequence at the recombination site between variable and joining genes to produce the observed protein structure. Alternatively, there may exist joining gene segments not yet detected. The study of antibody structure and diversity has long been of great interest in the field of immunology. The immunoglobulin molecule is composed of two polypeptide chains designated light (L) and heavy (H), each of which is encoded on a separate chromosome (1). Each of these two chains in turn is coded for by at least three distinct genetic regions termed variable (V), constant (C), and joining (J). The V regions of both H and L chains exhibit primary amino acid sequence differences that are responsible for the great variety of antigen binding specificities exhibited by vertebrate organisms. All L chain C regions may be divided into two classes, K and X; the corresponding region in heavy chains may represent several classes-i.e., jA y, a, 6, and e.Recent studies at both the protein (2-4) and nucleic acid levels (5, 6) have identified a third segment of the immunoglobulin chain, the J segment which bridges the V and C regions. The size and boundaries of this segment have been defined for mouse K chains and include the last residue in the third complementarity-determining region. A corresponding J segment has been identified in H chains by protein sequence determination (4, 7) and by nucleic acid analysis (8).For a number of years this laboratory has attempted to explore various aspects of antibody structure and diversity by analyzing groups of antigen-binding myeloma proteins. One such group is composed of proteins with binding specificity for 3(1,6)-linked galactan moieties. Six of these proteins have been studied in terms of specificity (9, 10), structure (3, 4, 11), and idiotypy (12). We have reported the L chain V region sequences from ...

Remarkably similar antigen receptors among a subset of patients with chronic lymphocytic leukemia

“…Fourth, the presence of a positively charged center to the antigen-binding pocket, provided by the side chain of arginine L96, and surrounded by an aromatic area and a ridge of polar residues, would imply that a negatively charged or electron-rich group exists in the epitope interactive with these BCRs (Figure 3). This, however, is not a necessity (41,53,59). Of the 199 completely sequenced antibodies with an arginine at L96 (14), we found that about 50% react with autoantigens.…”

“…Murine mAb's reactive with arsonate (Ars), dsDNA, and β-(1,6)-D-galactan exhibit an arginine or an isoleucine at position L96, respectively. These junctional amino acids are essential for binding to Ars (53), but not to β-(1,6)-D-galactan (59).…”

Diversity at the variable-joining region boundary of lambda light chains has a pronounced effect on immunoglobulin ligand-binding activity.

“…14) had not been reported in A chains. This detection Rudikoff et al (33) that the V-J boundary residue of K chains was a direct consequence of analysis of X chain contributions has no significant effect on hapten binding. They found that to ligand-binding activity.…”

Galactan-binding antibodies. Diversity and structure of idiotypes.

“…One such system being developed in our laboratory consists of antibodies with specificity for/3(1,6)-a-galactan moieties. A number of myeloma proteins demonstrating this specificity were initially characterized in terms of specificity (38,40), idiotypy (41), and primary sequence analysis (10,19). More recently we have generated a series of hybridoma proteins exhibiting the same specificity and have reported complete r chain V region sequences for 10 of these (37).…”