Kulp John L, Minamisawa Tamiko, Shiba Kiyotaka, Tejani Margaret, Evans John Spencer
Laboratory for Chemical Physics, New York University, New York, New York 10010, USA.
Langmuir. 2007 Mar 27;23(7):3857-63. doi: 10.1021/la062442f. Epub 2007 Feb 20.
Technological advances have facilitated the generation of artificial proteins that possess the capabilities of recognizing and binding to inorganic solids and/or controlling nucleation processes that form inorganic solids. However, very little is known regarding the structure of these interesting polypeptides and how their structure contributes to functionality. To address this deficiency, we report structural investigations of an artificial protein, p288, that self-assembles and controls the nucleation of simple salts and organic compounds into dendrite-like crystals. Under aqueous conditions at low pH and in the presence of high salt, p288 is conformationally labile and exists primarily as a random coil conformer in equilibrium with other undefined secondary structures, including polyproline type II and beta turn. We note that p288 can fold into either a partial beta strand (at neutral pH) or a predominantly alpha helical (in the presence of TFE) conformation. Solid-state 13C-15N NMR experiments also reveal that p288 in the lyophilized, hydrated state possesses some degree of nonrandom coil structure. These results indicate that p288 is conformationally labile but can undergo conformational transitions to a more stable structure when water solvent loss/displacement occurs and protein concentrations increase. We believe that conformational instability and the ability to adopt different structures as a function of different environmental conditions represent important molecular features that impact p288 supramolecular assembly and crystal nucleation processes.
技术进步促进了人工蛋白质的产生，这些人工蛋白质具有识别和结合无机固体和/或控制形成无机固体的成核过程的能力。然而，对于这些有趣的多肽的结构以及它们的结构如何对功能产生影响，我们知之甚少。为了解决这一不足，我们报告了对一种人工蛋白质p288的结构研究，该蛋白质能自我组装并控制简单盐类和有机化合物成核形成树枝状晶体。在低pH值的水性条件下且存在高盐时，p288的构象不稳定，主要以无规卷曲构象存在，并与其他未定义的二级结构处于平衡状态，包括多聚脯氨酸II型和β转角。我们注意到，p288可以折叠成部分β链（在中性pH值下）或主要为α螺旋（在TFE存在下）的构象。固态13C - 15N NMR实验还表明，冻干、水合状态下的p288具有一定程度的非无规卷曲结构。这些结果表明，p288的构象不稳定，但当发生水溶剂损失/置换且蛋白质浓度增加时，它可以经历构象转变形成更稳定的结构。我们认为，构象不稳定性以及根据不同环境条件采用不同结构的能力代表了影响p288超分子组装和晶体成核过程的重要分子特征。
