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

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Abstract
The amino acid sequence was determined for the variable (V) region of the .delta. 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 3rd 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 Ig. The V region sequence together with previous results for the C region give the complete sequence of the human .delta. chain WAH, which has 512 amino acid residues and a MW .apprxeq. 65,000. The human .delta. chain has 4 domains (V, C.delta.1, C.delta.2 and C.delta.3) and a long hinge region; by comparison, the mouse .delta. chain lacks a continuous segment of 135 residues, including half the hinge region and the entire C.delta.2 domain. The human and mouse .delta. chains also differ in the number, kind and location of GlcN and GalN glycans and probably in conformation and quaternary structure. There may be multiple forms of both secreted and membrane-bound IgD that differ in size, structure and function.