Independent folding of the variable and constant halves of a lambda immunoglobulin light chain

Optical rotatory dispersion and circular dichroism studies of a lambda immunoglobulin light chain and its variable and constant halves are reported. The two fragments, which have been extensively characterized, were isolated after proteolytic digestion of the lambda-chain. A dichroism band at 217 nm, previously found to be characteristic of all immunoglobulins, was given by both the variable and constant halves. In other respects, the fragments yielded clearly different spectra, reflecting differences in their conformations. Comparisons of the theoretical curves calculated for an equimolar mixture of the fragments with the corresponding curves measured for the lambda-chain showed that most of the minimal conformational changes accompany cleavage of the polypeptide into its halves. This suggests that in the intact light chain, the variable and constant parts exist as independently folded regions.