화학공학소재연구정보센터
Journal of the American Chemical Society, Vol.128, No.29, 9506-9517, 2006
Effects of temperature and salt concentration on the structural stability of human lymphotactin: Insights from molecular simulations
Extensive molecular dynamics (MD) simulations (similar to 70 ns total) with explicit solvent molecules and salt ions are carried out to probe the effects of temperature and salt concentration on the structural stability of the human Lymphotactin (hLtn). The distribution of ions near the protein surface and the stability of various structural motifs are observed to exhibit interesting dependence on the local sequence and structure. Whereas chloride association to the protein is overall enhanced as the temperature increases, the sodium distribution in the C-terminal helical region and, to a smaller degree, the chloride distribution in the same region are found higher at the lower temperature. The similar trend is also observed in nonlinear Poisson-Boltzmann calculations with a temperature-dependent water dielectric constant, once conformational averaging over a series of MD snapshots is done. The unexpected temperature dependence in the ion distribution is explained on the basis of the cancellation of association entropy for ion-side chain pairs of opposite-charge and like-charge characters, which have positive and negative contributions, respectively. The C-terminal helix is observed to partially melt whereas a short beta strand forms at the higher temperature with little salt dependence. The N-termal region, by contrast, develops partial helical structure at a higher salt concentration. These observed behaviors are consistent with solvent and salt screening playing an important role in stabilizing the canonical chemokine fold of hLtn.