gamma Heavy chain disease in man: cDNA sequence supports partial gene deletion model.

Abstract

Human y heavy chain disease (HCD) is characterized by the presence in serum of a short monoclonal Ig y chain unattached to light chains. Although most HCD proteins have internal deletions, in some the defect is NH2-terminal. The OMM v3 HCD serum protein is of the latter type, having undergone an extensive NH2-terminal deletion with a sequence starting within the hinge. A cell line synthesizing the OMM protein has enabled us to study the biogenesis ofthe abnormal molecule. In vitro translation ofisolated mRNA yields a protein containing a hydrophobic NH2-terminal leader sequence. In the intact cell, the precursor molecule is processed normally to yield a protein with an NH2-terminal sequence homologous to the beginning of the variable (V) region. The nucleotide sequence of cDNA prepared from the OMM mRNA encodes a 19-amino acid leader followed by the first 15 residues ofthe V region. An extensive internal deletion encompasses the remainder of the V and the entire CHI domain. Immediately following the short V region, there is information in the cDNA for the entire normal hinge. The primary synthetic product is thus an internally deleted molecule that undergoes postsynthetic degradation to yield the NH2-terminally deleted serum protein.The structure of the OMM mRNA suggests that the protein abnormality results from a partial gene deletion rather than defective splicing.In heavy chain disease (HCD), a naturally occurring human lymphoproliferative disorder, variant monoclonal Ig heavy (H) chain fragments are found in the patients' serum or urine. HCD proteins of the 'y class have been studied in detail, although those ofthe a and. y classes have also been described (1, 2). The abnormal serum proteins of the y class all show complete deletion of the CHi domain of the constant (C) region. Additional features separate the proteins into three types. Most ofthe variant molecules studied to date have a normal or aberrant NH2-terminal variable (V)-region sequence ofvariable size, followed by an extensive internal deletion encompassing most of the V region and the CHL domain. Normal structure usually resumes at the beginning ofthe hinge. In the second group, the deletion continues through the hinge, with normal sequence starting in the CH2 domain. Least frequently, y HCD proteins are found that lack the entire V and CHI domains. In such cases, the serum protein sequence starts within the hinge, and it is therefore unclear whether the molecules are of degradative or synthetic origin.A y3 HCD protein was isolated from the serum of patient OMM and shown to have a monomeric molecular weight of 40,000 and an unblocked NH2 terminus (3). It had undergone an extensive NH2-terminal deletion with a homogeneous sequence starting within the hinge. In addition to the HCD protein, the patient's serum also contained a homogeneous (y3)2A2 molecule with apparently normal H and light (L) chains (4). Because the HCD protein was NH2-terminally deleted, it was not possible to tell whether it was the product of partial proteolytic degrad...

DNA sequence variability of IGHG3 alleles associated to the main G3m haplotypes in human populations

“…G3m (21) is likely to be determined by a Pro?Leu mutation at position 291 (CH2 domain). The same conclusion was drawn from the analysis of the OMM protein 42,43 and a previous sequencing of CH2-CH3 domains. 13 We exclude the involvement of amino acid Asn384, because it is coded by one G3m 5,10,11,13,14 Mandenka sequence (M6), and of Arg435-Tyr436, because they are located on CH3: enzymatic digestions indicate that G3m (21) is detected on the Fc (CH2-CH3), but not on the Fc' (CH3) fragments.…”

Molecular basis of the cell-surface expression of immunoglobulin mu chain without light chain in human B lymphocytes.

“…In the case of BiP-H-chain association, BiP seems to require a site within the CH1 domain of H chains and is no longer associated with H chain after the L-chain-Hchain pairing process (6,8). Consistent with this scheme is the uniform deletion of all or part of the CH1 domain among the secreted human H* chains (4,(9)(10)(11)(12). As all transported H* chains thus far tested fail to interact with BiP with normal affinity (8), it has been suggested that such truncated H* chains can be secreted by virtue of the inability of BiP to recognize them and prevent their movement out of the ER.…”

“…Intracellular transport of the A* chains is thus unencumbered from the normal mechanism governing transport of native H chains, leading to the expression of the unusual pz-chain-only phenotype for cellsurface immunoglobulin. While it is known that both mouse and human CA1 domain-deleted A chains can be secreted without being paired with L chain (8)(9)(10)(11), the ability of these truncated ,u chains to be expressed at the cell surface is currently unknown.…”

“…A 19-mer synthetic oligonucleotide complementary to nucleotides [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] (CAl. 1) and an 18-mer synthetic oligonucleotide complementary to nucleotides 26-44 (CL1.3) of the human CIL1 exon (22) were used as primers to initiate cDNA synthesis (see Fig.…”

Articular, monoclonal γ3 heavy‐chain deposition disease: Characterization of a partially deleted heavy‐chain gene and its protein product synthesized in vivo and in vitro

“…In the previously reported case of patient OMM with ␥3 heavy-chain disease (2,(7)(8)(9), the deleted ␥3 protein present in serum started at the N-terminus of the hinge region (residue 226 in normal ␥3), whereas the complementary DNA (cDNA) and protein product of cloned cells, as well as that translated from the respective messenger RNA, showed that an additional segment consisting of the 14 N-terminal amino acid residues of V H plus a proline at position 15 was directly attached to the hinge. This apparent discrepancy was apparently caused by posttranslational proteolysis.…”