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

Molecular mechanisms of antibody somatic hypermutation

Functional antibody genes are assembled by V-D-J joining and then diversified by somatic hypermutation. This hypermutation results from stepwise incorporation of single nucleotide substitutions into the V gene, underpinning much of antibody diversity and affinity maturation. Hypermutation is triggered by activation-induced deaminase (AID), an enzyme which catalyzes targeted deamination of deoxycytidine residues in DNA. The pathways used for processing the AID-generated U:G lesions determine the variety of base substitutions observed during somatic hypermutation. Thus, DNA replication across the uracil yields transition mutations at C:G pairs, whereas uracil excision by UNG uracil-DNA glycosylase creates abasic sites that can also yield transversions. Recognition of the U:G mismatch by MSH2/MSH6 triggers a mutagenic patch repair in which polymerase eta plays a major role and leads to mutations at A:T pairs. AID-triggered DNA deamination also underpins immunoglobulin variable (IgV) gene conversion, isotype class switching, and some oncogenic translocations in B cell tumors.

Kappa marker typing with high-performance liquid chromatography: identification of kappa marker specific tryptic peptide from the kappa light chain of immunoglobulin G

Human serum immunoglobulin G was separated into its heavy and light chains by sodium dodecyl sulfate polyacrylamide gel electrophoresis and transferred electrophoretically to a polyvinylidenedifluoride membrane. Peptide fragments liberated from the light chain by in situ digestion with trypsin were then analyzed by reversed-phase high-performance liquid chromatography (HPLC). On comparing the HPLC patterns of these fragments derived from three major kappa marker (Km) types, two distinct peaks specific for the Km types were detected. Sequencing of the two specific peak peptides confirmed that they were identical to a stretch comprising residues 191-207 of the immunoglobulin kappa light chain, which contains valine/leucine allotypic variation at position 191.

Amino acid sequence of the variable region of a human mu chain: location of a possible JH segment

The complete amino acid sequence of th variable (V) region of the mu heavy chain of a human IgM immunoglobulin (Cam) has been determined. The strategy for sequence determination involved sequenator analysis of the CNBr cleavage products of the succinylated carboxymethylated Fab mu fragment, and of tryptic peptides of the CNBr polypeptides and thermolytic subpeptides. The variable region of this heavy chain (VH) belongs to the VHIII subgroup; it has greater than 70% homology with other VHIII sequences and contains the VHIII marker peptide, Phe-Thr-Ile-Ser-Arg (residues 67-71). As more sequences have been published, the number of subgroup-specific residues has diminished to the point that no position is absolutely subgroup specific. An analysis of the available human VH sequences in the V/C switch region showed the likelihood of a human JH segment (residues 101-113) analogous to the J segments in mouse light chains. The JH region is highly conserved, has striking homology to proposed mouse JH regions, and has significant homology to known mouse J lambda and J kappa segments.

The amino acid sequence of a human kappa light chain

The amino acid sequence of the light chain of the myeloma protein Dee was studied. The light chain is of the kappa type and of subgroup I. The variable part contains some substitutions that are unique and also some that have been observed already in other kappaI chains (repeated variants). Based on these repeated variants a subdivision of the kappaI subgroup is proposed.

Bence Jones proteins and light chains of immunoglobulins. II. Immunochemical differentiation and classification of kappa-chains

Three distinct classes of kappa light polypeptide chains have been detected immunochemically by an antiserum (R185) prepared against a kappa Bence Jones protein with a glutamyl amino terminal residue. This antiserum had specificity for kappa light chains with glutamyl amino terminal residues and differentiated kappa-chains with aspartyl amino terminal residues into two classes: the three kappa-chain classes have been designated as kappa(glu), kappa(aspII), and kappa(aspI). The ability of antiserum R185 to detect these antigenic differences on the intact immunoglobulin molecule, as well as on the isolated light chain or Bence Jones protein, made feasible the direct classification of type K myeloma proteins and M-macroglobulins (Waldenström). The multispecificity of the antiserum permitted the quantitation of type kappa(glu) light chains in normal, hypergammaglobulinemic, and hypogammaglobulinemic sera. Whereas the distribution of myeloma proteins and Bence Jones proteins in the kappa(glu) class correlated with the distribution of kappa(glu) chains in normal and hypergammaglobulinemic sera, the M-macroglobulins in the kappa(glu) class represented 90% of the total M-macroglobulins tested and revealed a marked divergence from the range of 24-31% of kappa(glu) immunoglobulins in normal sera. A preponderance of kappa(glu) chains was detected in the sera from patients with non-sex-linked hypogammaglobulinemia and represented 60-77% of the total type K light chain content. The controlled cleavage of a Bence Jones protein representative of each kappa-chain class into its variant half and constant half made possible the localization on the light polypeptide chain, the reactive sites for which antiserum R185 had specificity. The correlations between immunochemical and structural classification of kappa light chains are discussed.

On the location and structure of the active sites of antibody molecules

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