Clathrin Light Chains LCA and LCB are Similar, Polymorphic, and Share Repeated Heptad Motifs

The clathrin light chains fall into two major classes, LCA and LCB. In an intact clathrin triskelion, one light chain, of either class, is bound to the proximal segment of a heavy chain leg. Analysis of rat brain and liver complementary DNA clones for LCA and LCB shows that the two light chain classes are closely related. There appear to be several members of each class having deletions of varying length aligned at the same position. A set of ten heptad elements, characteristic of $\alpha $-helical coiled coils, is a striking feature of the central part of each derived amino acid sequence. These observations suggest a model in which the $\alpha $-helical segment mediates binding to clathrin heavy chains and the amino- and carboxyl-terminal segments mediate interactions with other proteins. They also suggest an explanation for the observed tissue-dependent size variation for members of each class.