Brain proteins interacting with the tetramerization region of non-erythroid alpha spectrin

The N-terminal region of non-erythroid alpha spectrin (Sp alpha II) is responsible for interacting with its binding partner, beta spectrin, to form functional spectrin tetramers. We used a yeast-two-hybrid system, with an N-terminal segment of alpha spectrin representing the functional tetramerization site, as a bait to screen human brain c-DNA library for proteins that interact with the alpha spectrin segment. In addition to several beta spectrin isoforms, we identified 14 proteins that interact with Sp alpha II. Seven of the 14 were matched to 6 known proteins: Duo protein, Lysyl-tRNA synthetase, TBP associated factor 1, two isoforms (b and c) of a protein kinase A interacting protein and Zinc finger protein 333 (2 different segments). Four of the 6 proteins are located primarily in the nucleus, suggesting that spectrin plays important roles in nuclear functions. The remaining 7 proteins were unknown to the protein data base. Structural predictions show that many of the 14 proteins consist of a large portion of unstructured regions, suggesting that many of these proteins fold into a rather flexible conformation. It is interesting to note that all but 3 of the 14 proteins are predicted to consist of one to four coiled coils (amphiphilic helices). A mutation in Sp alpha II, V22D, which interferes with the coiled coil bundling of Sp alpha II with beta spectrin, also affects Sp alpha II interaction with Duo protein, TBP associated factor 1 and Lysyl-tRNA synthetase, suggesting that they may compete with beta spectrin for interaction with Sp alpha II. Future structural and functional studies of these proteins to provide interaction mechanisms will no doubt lead to a better understanding of brain physiology and pathophysiology.