| Abstract
| - A truncated version of the GCN4 coiled-coil peptide has been studied by ultraviolet resonance Raman (UVRR)spectroscopy with 197 nm excitation, where amide modes are optimally enhanced. Although the CD meltingcurve could be satisfactorily described with a two-state transition having Tm = 30 °C, singular valuedecomposition of the UVRR data yielded three principal components, whose temperature dependence implicatesan intermediate form between the folded and unfolded forms, with formation and melting temperatures of 10and 40 °C. Two α-helical amide III bands, at 1340 and 1300 cm-1, melted out selectively at 10 and 40 °C,respectively, and are assigned to hydrated and unhydrated helical regions. The hydrated regions are proposedto be melted in the intermediate form, while the unhydrated regions are intact. Time-resolved UVRR spectrafollowing laser-induced temperature jumps revealed two relaxations, with time constants of 0.2 and 15 μs.These are suggested to reflect the melting times of hydrated and unhydrated helices. The unhydrated helicalregion may be associated with a 14-residue “trigger” sequence that has been identified in the C-terminal halfof GCN4. Dehydration of helices may be a key step in the folding of coiled-coils.
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