Amino acid sequence of the first constant region domain and the hinge region of the delta heavy chain of human IgD.

Abstract

Amino acid sequences were determined for the 1st constant (C) region domain (C.delta.1) and the hinge region of the .delta. H chain of human IgD WAH and for the adjacent COOH-terminal portion of the variable (V) region, including the joining (JH) region. Together with the sequence of the Fc fragment already reported, this establishes the complete amino acid sequence of the C region of the human .delta. chain and confirms the presence of 3 C region domains in human IgD. Although the CH1 domains of the 5 classes of human H chains have the expected degree of homology (.apprxeq. 30%), the homology of the C.delta.1 domains of the human and mouse chains is less than that exhibited by the CH1 domains of other pairs of human and mouse H chains. The hinge region of the human .delta. chain has an unusual structure; the NH2-terminal half has 4 (or 5) GalN oligosaccharides attached, whereas the COOH-terminal half lacks carbohydrate, is dissimilar in sequence and has a high charge. A computer search verified that the GalN-rich segment has a high degree of identity in sequence with the middle portion of the human C.mu.2 domain and that the high-charge segment is related to the same sequence. The 2 segments of the human .delta. hinge may have a common evolutionary origin and may have arisen by duplication and independent mutation of a hinge exon derived from the ancestral gene for the C.mu.2 domain.