Correlation between fragmented immunoglobulin genes and heavy chain deletion mutants

The amino acid sequence of a monoclonal gamma 3-heavy chain from a patient with articular gamma-heavy chain deposition disease

Abnormal deposition of proteins, including monoclonal immunoglobulin gamma-heavy chains, may cause tissue damage and organ dysfunction. We here report the amino acid sequence of the free gamma-heavy chains present in serum and urine of the first reported case (patient G. L.) of synovial heavy chain deposition disease. The protein was heavily deleted and consisted of the hinge, in addition to the CH2 and CH3 domains, in a dimeric form, thus lacking its variable domain as well as the CH1 domain. The sequence was consistent with the gamma 3 subclass (gamma 3GL). Gm typing revealed the gamma 3 allotypes G3m(b0) and G3m(b1) in accordance with the residues Pro123, Phe128, Thr171 and Phe268 in gamma 3GL. Furthermore, the gamma 3GL molecule was glycosylated at Asn in position 129. Finally, the gamma 3GL protein was shown to contain a typical binding site for the first complement component, C1q, namely the residues Glu150, Lys152 and Lys154, with the potential of binding and activating complement, causing tissue damage following deposition.

Gamma heavy chain disease in man. Genomic sequence reveals two noncontiguous deletions in a single gene

A genomic clone was isolated from a human lymphoid cell line which synthesized an NH2-terminally deleted gamma 3 heavy chain disease protein. Nucleotide sequence analysis revealed a normal sequence from 310 bp 5' to the initiator ATG through the codon for VH amino acid 14. Amino acid 15 was derived from the codon for the last J4 amino acid. Thus, the clone contained a deletion of the codons for the VH region beyond amino acid 14, as well as those for the entire D region and most of the J coding region. Some sequence abnormalities were observed in the 400 bp after the deletion. Beyond this, there was excellent homology to published J and intervening sequences, including those containing the enhancer elements. The 1,200-bp switch region was abruptly interrupted by a sequence corresponding to the 3' one-third of CH1. Thus, a second deletion eliminated the acceptor splice site at the 5' end of CH1. When splicing of the primary RNA transcript occurred, the truncated VH region was joined via the J4 donor splice site to the next available acceptor site 5' to the first hinge exon. Hence, the aberrant serum protein was the product of two deletions and a splice correction as well as postsynthetic NH2-terminal proteolysis.

A new case of gamma-heavy chain disease (LIA protein) with deletion of the hinge region

An IgG1K monoclonal component with abnormal covalent H and L chains structure (LIA protein) was identified during a systematic screening of myeloma proteins by means of non-reducing/reducing SDS-polyacrylamide gel electrophoresis. Using immunochemical and immunogenetic analysis the mutation was characterized as a hinge region deletion, with loss of L-H and H-H disulphide bridges and direct L-L bonds. Moreover, non-expression of the G1m(z) allotype suggested that the deletion might start at residue 216, a preferential site previously observed in other HCD proteins. This feature is in agreement with the discontinuous structure of immunoglobulin CH genes and suggests that an abnormal switch mechanism is responsible for the deletion.

The generation of antibody diversity

By their nature, antibody molecules exhibit a wide range of binding specificities. The antigen-binding properties of the antibody reside entirely in the amino-terminal portion of the molecule, termed the variable domain. Structurally, the combining site specificity is determined by the amino-acid residues within 6 short lengths, 3 each in the heavy and light chains, of usually variable sequence. The hypervariability of 2 of these lengths arises from the somatic recombination of short gene segments into a single stretch of mRNA which encodes the entire variable region of 1 polypeptide chain. For example, a V gene segment that codes for most of the variable portion of a light chain, can combine with one of a number of much shorter J gene segments to create the complete variable region gene. In heavy chain genes, a third element, the D gene segment, increases the potential for diversity even further. A mechanism has been proposed by which variability occurs at the point where 2 gene segments join. Thus, a large part of the generation of antibody diversity occurs in the somatic recombination of small genetic elements.

Unusual heavy chains of human IgG immunoglobulins: rearrangements of the ch domain exons

Unusual combinations--unexpected sets, excess of lack--of antigenic determinants, or Gm allotypes, on the constant regions of the heavy chains of the human IgG1 and IgG3 immunoglobulins are accounted for in terms of genetic events (exchanges, duplications and deletions) involving the DNA sequences, or exons, coding for the three CH1-, CH2- and CH3 domains of the gamma 1 and gamma 3 chains. Equal and unequal cross-overs at the level of the introns without damage to the CH exons are postulated.

IgA proteases of two distinct specificities are released by Neisseria meningitidis

Strains of Neisseria meningitidis produce two distinct extracellular IgA proteases that cleave the human IgA1 heavy chain at different points within the hinge region. Type 1 protease cleaves the prolyl-seryl peptide bond at position 237-238; type type 2 protease cleaves the prolyl-threonyl bond two residues amino terminal to that bond attacked by type 1 enzyme. Each meningococcal isolate elaborates only one of these two enzymes, and the type of protease produced correlates with certain serogroups: group A yielding only type 1, and groups X and Y only type 2 enzyme. In addition, analysis of amino acid sequences of human alpha-chain proteins reveals that the repeating octapeptide characteristic of the IgA1 hinge region is actually triplicated.

Primary structure of human gamma 3 immunoglobulin deletion mutant: gamma 3 heavy-chain disease protein Wis

The complete sequence of a gamma 3 heavy-chain disease (HCD) protein Wis is presented. The molecule is a dimer of a 289-residue chain linked by 12 disulfide bonds. Protein Wis has an unusual amino terminus, followed by a deletion of most of the VH domain. After a small stretch homologous to the VC joining region, there is a second deletion which ends at the beginning of the quadruplicated hinge. Two carbohydrate groups are linked to Asn-6 and -140. the molecule has an extra interchain disulfide bridge at position 7 in addition to the 11 normally present in the quadruplicated hinge. The previously noted homology to the gamma 1 heavy chain is striking; from positions 224 to 234, protein Wis resembles gamma 1 Nei [Ponstingl, H., & Hilschmann, N. (1976) Hoppe-Seyler's Z. Physiol. Chem. 357, 1571--1604] except for a serine which replaces Asn at position 227. The results, taken together with studies of other immunoglobulin heavy-chain deletion mutants, support the suggestion that the different domains and interdomain regions of human H chains are coded for by different gene segments and that the deleted proteins reflect alterations in the recombination of different genes and/or the splicing of heterogeneous nuclear messenger ribonucleic acid (hn mRNA).

An immunoglobulin deletion mutant with implications for the heavy-chain switch and RNA splicing

The IF2 immunoglobulin mutant is a DNA deletion of one coding segment and large sections of the flanking intervening sequences. The deletion results in a new splicing pattern and starts in a DNA region containing tandemly repeated sequences which may carry heavy-chain class switch signals.