Doig A J
Department of Biochemistry and Applied Molecular Biology, UMIST, P.O. Box 88, Manchester M60 1QD, UK.
Biophys Chem. 1996 Oct 30;61(2-3):131-41. doi: 10.1016/s0301-4622(96)02180-1.
The absolute Gibbs energy, enthalpy and entropy of each of the internal rotations found in protein side chains has been calculated. The calculation requires the moments of inertia of the side chains about each bond, the potential energy barrier and the symmetry number and gives the maximum possible thermodynamic consequences of restricting side chain motion when a protein folds. Hindering side chain internal rotations is unfavourable in terms of Gibbs energy and entropy; it is enthalpically favourable at 0 K. At room temperature, it is estimated that the adverse entropy of hindering buried side chain internal rotation is only 25% of the absolute entropy. The difference between absolute entropies in the folded and unfolded states gives the entropy change for folding. The estimated Gibbs energy change for restricting each residue correlates moderately well with the probability of that residue being found on the folded protein surface, rather than in the protein interior (where motion is restricted).
已计算出蛋白质侧链中每个内旋转的绝对吉布斯自由能、焓和熵。该计算需要侧链围绕每个键的转动惯量、势能垒和对称数，并给出了蛋白质折叠时限制侧链运动可能产生的最大热力学结果。就吉布斯自由能和熵而言，阻碍侧链内旋转是不利的；在0 K时，焓变是有利的。在室温下，据估计，阻碍埋藏侧链内旋转的不利熵仅为绝对熵的25%。折叠态和未折叠态的绝对熵之差给出了折叠的熵变。限制每个残基的吉布斯自由能变化估计值与该残基出现在折叠蛋白质表面而非蛋白质内部（运动受限处）的概率具有适度的相关性。
