Ferreira Helen E, Drobny Gary P
Department of Chemistry, University of Washington, Box 351700, Seattle, Washington 98195.
Biointerphases. 2017 Jun 27;12(2):02D418. doi: 10.1116/1.4986907.
In nature, organisms including diatoms, radiolaria, and marine sponges use proteins, long chain polyamines, and other organic molecules to regulate the assembly of complex silica-based structures. Here, the authors investigate structural features of small peptides, designed to mimic the silicifying activities of larger proteins found in natural systems. LKα14 (Ac-LKKLLKLLKKLLKL-C), an amphiphilic lysine/leucine repeat peptide with an α-helical secondary structure at polar/apolar interfaces, coprecipitates with silica to form nanospheres. Previous C magic angle spinning studies suggest that the tetrameric peptide bundles that LKα14 is known to form in solution may persist in the silica-complexed form, and may also function as catalysts and templates for silica formation. To further investigate LKα14 aggregation in silica, deuterium solid-state nuclear magnetic resonance (H ssNMR) was used to establish how leucine side-chain dynamics differ in solid LKα14 peptides isolated from aqueous solution, from phosphate-buffered solution, and in the silica-precipitated states. Modeling the H ssNMR line shapes probed the mechanisms of peptide preaggregation and silica coprecipitation. The resulting NMR data indicates that the peptide bundles in silica preserve the hydrophobic interior that they display in the hydrated solid state. However, NMR data also indicate free motion of the leucine residues in silica, a condition that may result from structural deformation of the aggregates arising from interactions between the surface lysine side chains and the surrounding silica matrix.
在自然界中，包括硅藻、放射虫和海洋海绵在内的生物体利用蛋白质、长链多胺和其他有机分子来调节基于二氧化硅的复杂结构的组装。在此，作者研究了小肽的结构特征，这些小肽旨在模拟天然系统中发现的较大蛋白质的硅化活性。LKα14（Ac-LKKLLKLLKKLLKL-C）是一种两亲性赖氨酸/亮氨酸重复肽，在极性/非极性界面处具有α-螺旋二级结构，它与二氧化硅共沉淀形成纳米球。先前的碳魔角旋转研究表明，已知LKα14在溶液中形成的四聚体肽束可能以与二氧化硅复合的形式持续存在，并且还可能作为二氧化硅形成的催化剂和模板。为了进一步研究LKα14在二氧化硅中的聚集情况，使用氘固态核磁共振（H ssNMR）来确定从水溶液、磷酸盐缓冲溶液中分离出的固态LKα14肽以及二氧化硅沉淀状态下亮氨酸侧链动力学的差异。对H ssNMR线形进行建模探究了肽预聚集和二氧化硅共沉淀的机制。所得的核磁共振数据表明，二氧化硅中的肽束保留了它们在水合固态中呈现的疏水内部。然而，核磁共振数据也表明二氧化硅中亮氨酸残基存在自由运动，这种情况可能是由于表面赖氨酸侧链与周围二氧化硅基质之间的相互作用导致聚集体结构变形所致。
