Chemical structure of light chains: amino acid sequence of type K Bence-Jones proteins

Bence-Jones proteins are the light chains of the autologous myeloma globulin and are analogous to the light chains of normal human immunoglobulins. Peptide mapping has demonstrated that Bence-Jones proteins share a fixed portion of their sequence (the ‘constant’ portion) and also have a mutable part (the ‘variable’ portion). Sequence analysis and ordering of the tryptic and chymotryptic peptides has provided the tentative complete amino acid sequence of one Bence-Jones protein of antigenic type K. Comparison with partial sequence data for other type K Bence-Jones proteins has revealed many structural differences in the amino terminal half of the molecules, but only one structural difference in the carboxyl terminal half. The latter is strongly correlated with the Inv genetic factor. The points of interchange in the amino terminal half occur in clusters close to the half cystine residues and the ‘switch peptide’ (positions 102 through 105), after which the sequence becomes essentially invariant. This suggests that the major areas subject to sequence variation are part of a single topographical region which may define a portion of the antigen combining site in the light chains of antibodies. Many, but not all, the amino acid interchanges are compatible with a single point mutation. As yet, no single mutational theory suffices to explain the manifold differences in structure of the light chains. Such structural variation, however, could result from the presence of many related genes.

Immunoglobulin structure: variation in the sequence of Bence Jones proteins

Analysis of the amino acid sequence of one Bence Jones protein is almost comtplete. Many points of interchange occur in the amino terminal. portion of the molecule relative to partial-sequence data for other proteins. Most, but not all, are, compartible with one-step mutations. Such structural variation in immunoglobulin light chains may result from many related genes.

Immunoglobulin structure: partial amino acid sequence of a Bence Jones protein

Sequence analysis and ordering of the soluble tryptic peptides of one Bence Jones protein and comparison with partial sequence data for another have revealed many structural differences in the half of the molecule with the terminal amino group, but only one structural difference in the half of the molecule having the terminal carboxyl group. Somatic chromosomal rearrangements may effect such changes and account for variability in antibody structure.