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Temperature-dependent dynamics of the villin headpiece helical subdomain, an unusually small thermostable protein.

Abstract：

:(15)N spin relaxation experiments were used to measure the temperature-dependence of protein backbone conformational fluctuations in the thermostable helical subdomain, HP36, of the F-actin-binding headpiece domain of chicken villin. HP36 is the smallest domain of a naturally occurring protein that folds cooperatively to a compact native state. Spin-lattice, spin-spin, and heteronuclear nuclear Overhauser effect relaxation data for backbone amide (15)N spins were collected at five temperatures in the range of 275-305 K. The data were analyzed using a model-free formalism to determine generalized order parameters, S, that describe the distribution of N-H bond vector orientations in a molecular reference frame. A novel parameter, Lambda=dln(1-S)/dln T is introduced to characterize the temperature-dependence of S. An average value of Lambda=4.5 is obtained for residues in helical conformations in HP36. This value of Lambda is not reproduced by model potential energy functions commonly used to parameterize S. The maximum entropy principle was used to derive a new model potential function that reproduces both S and Lambda. Contributions to the entropy, S(r), and heat capacity, C(r)(p), from reorientational conformational fluctuations were analyzed using this potential energy function. Values of S(r) show a qualitative dependence on S similar to that obtained for the diffusion-in-a-cone model; however, quantitative differences of up to 0.5k, in which k is the Boltzmann constant, are observed. Values of C(r)(p) approach zero for small values of S and approach k for large values of S; the largest values of C(r)(p) are predicted to occur for intermediate values of S. The results suggest that backbone dynamics, as probed by relaxation measurements, make very little contribution to the heat capacity difference between folded and unfolded states for HP36.

journal_name

J Mol Biol

journal_title

Journal of molecular biology

authors

Vugmeyster L,Trott O,McKnight CJ,Raleigh DP,Palmer AG 3rd

doi

10.1016/S0022-2836(02)00537-5

keywords:

subject

Has Abstract

pub_date

2002-07-19 00:00:00

pages

841-54

issue

eissn

0022-2836

issn

1089-8638

pii

S0022-2836(02)00537-5

journal_volume

320

pub_type

杂志文章

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Temperature-dependent dynamics of the villin headpiece helical subdomain, an unusually small thermostable protein.