Double mutant cycle analysis was employed to ascertain the role of intra- and interchain salt-bridges in the folding and stability of the dimeric coiled-coil peptide, GCN4-p1, the 33-residue leucine zipper domain of the transcriptional activator GCN4. Equilibrium circular dichroism studies of the urea-induced unfolding reaction at neutral pH revealed that both types of ionic interactions, localized primarily in the N-terminal portion of the molecule, enhance the stability of the native coiled-coil. By contrast, comparable stopped-flow circular dichroism studies indicate that the salt-bridge interactions, with one possible exception, are not well formed in the transition state for folding. Although the E22Q/R25A double mutant failed to fold, fragmentation studies suggest that the E22/R25 intramolecular salt-bridge may play a critical role in stabilizing C-terminal nascent helices that drive the association reaction. The remaining salt-bridges appear to stabilize the parallel-stranded coiled-coil architecture of GCN4-p1 only after the peptide traverses the rate-limiting, dimeric transition state. Study holds ProTherm entries: 17015, 17016, 17017, 17018, 17019, 17020, 17021, 17022, 17023, 17024, 17025, 17026, 17027, 17028, 17029 Extra Details: Pseudo wild type M2V. circular dichroism spectroscopy; electrostatics; ionic interactions; leucine zipper peptides; protein folding kinetics
Submitter: Connie Wang
Submission Date: April 24, 2018, 8:49 p.m.