Complete amino acid sequence of the delta heavy chain of human immunoglobulin D.

Abstract

We have determined the amino acid sequence of the variable (V) region of the 8 heavy (H) chain of human IgD isolated from the plasma of myeloma patient WAH. This V region is unusual in its amino end group (arginine) and in its length (129 residues). The length is due to 10 insertions in the third complementarity-determining region (CDR3). A computer search showed that no reported CDR3-joining region (-JH) sequences are identical and that they appear to be unrelated to the constant (C) region sequences of immunoglobulins. The V region sequence together with our previous results for the C region give the complete sequence of the human 8 chain WAH, which has 512 amino acid residues and a Mr 65,000. The human 8 chain has four domains (V, C81, C82, and C83) and a long hinge region; by comparison, the mouse 8 chain lacks a continuous segment of 135 residues, including half the hinge region and the entire C82 domain. The human and mouse 8 chains also differ in the number, kind, and location ofGlcN and GalN glycans and probably in conformation and quaternary structure. These and other considerations suggest that there may be multiple forms of both secreted and membranebound IgD that differ in size, structure, and function.Although sequence data have been published for more than 50,000 amino acid residues of immunoglobulins of various classes and species, until recently (1-8) little was known about the amino acid sequence of human IgD. The reasons include: (i) the low concentration of serum IgD except in rare patients with multiple myeloma, (ii) the apparent lack of a characteristic antibody activity or effector function, (iii) the extreme sensitivity of IgD to "spontaneous" proteolytic degradation (1, 9), and (iv) the unusual structure of the hinge region, which presented difficult technical problems for its determination (5, 6). However, mounting evidence that this minor class ofcirculating immunoglobulins has a major function as an antigen receptor on the membrane of B lymphocytes (10, 11) led us to undertake determination of the complete primary structure of human IgD. We have reported the complete amino acid sequence of the Fc region (2) and of the C81 and hinge regions (3), which together constitute the entire constant (C) region ofthe 8 chain of the myeloma protein WAH. Here, we report the structure ofthe variable (V) region ofthe heavy (H) chain (the VH region), which completes the amino acid sequence of the 8 H chain; in work to be reported separately, we have determined the entire sequence ofthe A light (L) chain, which completes the structure of a human IgD molecule.Interest in the structure of IgD was stimulated by evidence that it functions as a major receptor on the surface of B lymphocytes, where it is coexpressed with IgM after antigen capture triggers cell differentiation (10, 11). Like IgM, IgD exists in two forms: sIgD, which is secreted into the serum, and mIgD, which is bound to the B-cell membrane. Cloning studies (12)(13)(14)(15)(16) have shown that the A& and 8 structural genes may both b...

The Glycosylation and Structure of Human Serum IgA1, Fab, and Fc Regions and the Role of N-Glycosylation on Fcα Receptor Interactions

“…In addition, each site may contain a range of oligosaccharides. This complex range of glycosylated variants may also exist in IgD, where variable site occupancy has been reported (61,62). The finding that certain myeloma serum IgA1 proteins are glycosylated at all five serine residues (16) may be the result of an up-regulation of N-acetyl-galactosaminyltransferase or a modification in its specificity.…”

The Glycosylation of Human Serum IgD and IgE and the Accessibility of Identified Oligomannose Structures for Interaction with Mannan-Binding Lectin

“…IgD has three N-linked glycosylation sites (Fig. 1 (27). Studies of a myeloma IgD protein (23) found that Asn 354 in the C H 2 domain was occupied by oligomannose structures.…”

O-Glycosylation of Serum IgD in IgA Nephropathy

“…IgD, like IgA1, has a hinge region, and although the amino acid sequences of the two isotypes differ (20,21), they both carry approximately five O-glycan moieties per heavy chain. Hitherto, the O-glycosylation of IgD in IgAN has not been investigated, but this would be informative, as demonstration of an abnormality in both IgA1 and IgD O-glycosylation would suggest that the defect arises early in B cell development and may affect all B cells, whereas its restriction to IgA1 alone would indicate a later and possibly population-specific origin.…”