Complete covalent structure of a human immunoglobulin D: sequence of the lambda light chain.

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Abstract
The amino acid sequence of the .lambda. L chain of human IgD WAH was determined. Together with the sequence of the .delta. H chain already reported, this establishes the complete covalent structure of a human IgD. The sequence determination was greatly aided by the ability to use high-pressure liquid chromatography to purify large peptides, including 1 large fragment extending from Ser-81 through the carboxyl terminus. The IgD molecule is a 4-chain monomer of MW .apprxeq. 176,000; it consists of 2 .lambda. chains (each of 214 residues, MW = 22.893) and 2 .delta. chains (each of 512 residues, MW .apprxeq. 65,000, including carbohydrate), and, unlike murine IgD, it contains 2 C.delta.2 domains. A computer-assisted search using the J (joining) segment of the WAH .lambda. chain as a test piece showed a close evolutionary relationship of human and mouse J.lambda. regions and suggested that germ-line J.lambda. genes in the 2 species are very similar if not identical. DNA segments encoding J.lambda., J.kappa. and JH appear to have had a common evolutionary origin, and, surprisingly, JH seems closer to J.lambda. than does J.kappa.