Liu Susan M, Haynes Charles A
The Biotechnology Laboratory and The Department of Chemical and Biological Engineering, University of British Columbia, 237 Wesbrook Building, Vancouver, BC V6T 1Z3, Canada.
J Colloid Interface Sci. 2005 Apr 1;284(1):7-13. doi: 10.1016/j.jcis.2004.09.064.
Dynamic Monte Carlo (DMC) simulations of the adsorption of simple protein-like chains are used to more clearly define the molecular basis for the dependence of adsorption thermodynamics on the stability of the unique lowest-energy "native state" conformation of the chain. Arai and Norde were among the first to show that proteins of low native-state stability strongly denature upon adsorption to weakly attractive sorbent surfaces, while relatively modest changes in conformation are observed in stable proteins under identical adsorption conditions. When the protein has a low native-state stability, favorable adsorption entropies are typically observed in such systems, leading to the general belief that the chain gains conformational entropy during adsorption through a net reduction in intramolecular interactions specific to the native-state structure. Analysis of energy landscapes generated from our DMC simulation results show that a net loss in specific intramolecular interactions can lead to a positive delta(ads)S under certain adsorption conditions. However, the influence of chain conformation on delta(ads)S is found to correlate more directly with the manner in which the unique states of the system are distributed among the energy levels available to the adsorbed chain. Delta(ads)S is found to tend toward a maximum for adsorption processes described by thermally averaged energy landscapes in which the energy levels carrying the highest Boltzmann weights have a high degree of conformational degeneracy. This condition is met when the average interaction energy between the chain and the sorbent equals that between two hydrophobic segments of the chain.
利用动态蒙特卡罗(DMC)模拟简单的类蛋白质链吸附过程,以便更清晰地确定吸附热力学对链的唯一最低能量“天然态”构象稳定性依赖性的分子基础。荒井和诺德是最早表明低天然态稳定性的蛋白质在吸附到弱吸引力吸附剂表面时会强烈变性的人之一,而在相同吸附条件下,稳定蛋白质的构象变化相对较小。当蛋白质具有低天然态稳定性时,在这类系统中通常会观察到有利的吸附熵,这导致人们普遍认为链在吸附过程中通过净减少天然态结构特有的分子内相互作用而获得构象熵。对我们的DMC模拟结果生成的能量景观分析表明,在某些吸附条件下,特定分子内相互作用的净损失会导致正的δ(ads)S。然而,发现链构象对δ(ads)S的影响与系统的独特状态在吸附链可用能级之间的分布方式更直接相关。对于由热平均能量景观描述的吸附过程,发现δ(ads)S趋向于最大值,在这种景观中,具有最高玻尔兹曼权重的能级具有高度的构象简并性。当链与吸附剂之间的平均相互作用能等于链的两个疏水链段之间的相互作用能时,就满足了这一条件。