An unlocking/relocking barrier in conformational fluctuations of villin headpiece subdomain

• DOI: 10.1073/pnas.0910001107
• Publication Date: 2010-03-02T04:55:41Z
• Authors: Andreas Reiner; Peter Henklein; Thomas Kiefhaber
• Keywords: Conformational change

A reversible structural unlocking reaction, in which the close-packed van der Waals interactions break cooperatively, has been found for villin headpiece subdomain (HP35) using triplet-triplet-energy transfer to monitor conformational fluctuations from equilibrium. Unlocking is associated with an unfavorable enthalpy change (Δ H 0 = 35 ± 4 kJ/mol) nearly compensated free energy by entropy S 112 20 J·mol -1 ·K ). The reaction a time constant of about 1 μs at 5 °C and enthalpy-limited activation 32 kJ/mol large Arrhenius preexponential factor 7.5 × 10 11 s . In unlocked state fast local fluctuation 170 ns low barrier 17 leads unfolding C-terminal helix its undocking core. On much slower scale, global occurs state. These results suggest that native protein structures are locked into conformations amplitude motions. Large scale motions require initial step leading properties dry molten globule. experiments additionally yielded information on dynamics loop formation between different positions unfolded HP35. Comparison unstructured model peptides indicates slightly decelerated kinetics region points residual, nonrandom structure. Dynamics long-range formation, contrast, not influenced residual structure, argues against as molecular origin ultrafast folding