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Daniel Otzen

Conformational plasticity in folding of the split β-α-β protein S6: Evidence for burst-phase disruption of the native state

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An increasing number of folding studies of two-state proteins shows that point mutations sometimes change the kinetic m-values, leading to kinks and curves in the chevron plots. The molecular origin of these changes is yet unclear although it is speculated that they are linked to structural rearrangement of the transition state or to accumulation of meta-stable intermediates. To shed more light on this issue, we present here a combined m and φ-value analysis of the split β-α-β protein S6. Wild-type S6 displays classical two-state kinetics with v-shaped chevron plot, but a majority of its mutants display distinct m-value changes or curved chevrons. We observe that this kinetic aberration of S6 is linked to mutations that are clustered in distinct regions of the native structure. The most pronounced changes, i.e. decrease in the m-value for the unfolding rate constant, are seen upon truncation of interactions between the N and C termini, whereas mutations in the centre of the hydrophobic core show smaller or even opposed effects. As a consequence, the calculated φ-values display a systematic increase upon addition of denaturant. In the case of S6, the phenomenon seems to arise from a general plasticity of the different species on the folding pathway. That is, the structure of the denatured ensemble, the transition state, and the native ground-state for unfolding seem to change upon mutation. From these changes, it is concluded that interactions spanning the centre of the hydrophobic core form early in folding, whereas the entropically disfavoured interactions linking the N and C termini consolidate very late, mainly on the downhill-side of the folding barrier.

Original languageEnglish
JournalJournal of Molecular Biology
Pages (from-to)613-627
Number of pages15
Publication statusPublished - 1 Jan 2002

    Research areas

  • Curved chevron plots, Phi-value analysis, Protein folding, Protein plasticity, Transition state, Unfolding intermediate

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