Folding and Misfolding of the Potassium Channel Pore Domain during Assembly and Tetramerization

This thesis connects the dynamics of Kv1.2 and KcsA potassium channel pore domain monomers to the kinetics of tetramerization. In simulations, monomers adopt multiple conformations with the three helices folded. NMR studies also find the monomers to be dynamic and structurally heterogeneous. However, a KcsA construct with a disulfide bridge engineered between the two transmembrane helices has an NMR spectrum with well-dispersed peaks, suggesting that the monomer can be locked into a native-like conformation. During tetramerization, FRET results indicate that monomers rapidly oligomerize upon insertion into liposomes, forming a dense protein-rich phase. Folding within this protein-rich phase occurs along separate fast and slow routes, with $\tau_{f}$ $\sim$ 40 and 1500 seconds, respectively. In contrast, constructs bearing the disulfide bond mainly fold via the faster pathway, suggesting that maintaining the TM helices in their native orientation reduces misfolding. Interestingly, folding is concentration independent in spite of the tetrameric nature of the channel, indicating that the rate-limiting step is unimolecular and occurs after monomer association in protein-rich phase. Finally, despite its name, the addition of KcsA's C-terminal ``tetramerization" domain does not improve the kinetics of tetramerization.