Biological mineralization of tissues in living organisms relies on proteins that preferentially nucleate minerals and control their growth. This process is often referred to as "templating," but this term has become generic, denoting various proposed mineral-organic interactions including both chemical and structural affinities. Here, we present an approach using self-assembled networks of elastin and fibronectin fibers, similar to the extracellular matrix. When induced onto negatively charged sulfonated polystyrene surfaces, these proteins form fiber networks of approximately 10-mum spacing, leaving open regions of disorganized protein between them. We introduce an atomic force microscopy-based technique to measure the elastic modulus of both structured and disorganized protein before and during calcium carbonate mineralization. Mineral-induced thickening and stiffening of the protein fibers during early stages of mineralization is clearly demonstrated, well before discrete mineral crystals are large enough to image by atomic force microscopy. Calcium carbonate stiffens the protein fibers selectively without affecting the regions between them, emphasizing interactions between the mineral and the organized protein fibers. Late-stage observations by optical microscopy and secondary ion mass spectroscopy reveal that Ca is concentrated along the protein fibers and that crystals form preferentially on the fiber crossings. We demonstrate that organized versus unstructured proteins can be assembled mere nanometers apart and probed in identical environments, where mineralization is proved to require the structural organization imposed by fibrillogenesis of the extracellular matrix.

译文

生物体组织的生物矿化依赖于优先使矿物质成核并控制其生长的蛋白质。此过程通常称为 “模板”,但该术语已成为通用术语,表示各种拟议的矿物-有机相互作用,包括化学和结构亲和力。在这里,我们提出了一种使用弹性蛋白和纤连蛋白纤维的自组装网络的方法,类似于细胞外基质。当在带负电荷的磺化聚苯乙烯表面上诱导时,这些蛋白质形成约10-mum间距的纤维网络,在它们之间留下无序蛋白质的开放区域。我们介绍了一种基于原子力显微镜的技术,用于在碳酸钙矿化之前和过程中测量结构化和杂乱无章的蛋白质的弹性模量。在矿化的早期阶段,矿物引起的蛋白质纤维的增稠和硬化得到了清楚的证明,早在离散的矿物晶体足够大以通过原子力显微镜成像之前。碳酸钙选择性地使蛋白质纤维变硬,而不会影响它们之间的区域,从而强调了矿物质与有组织的蛋白质纤维之间的相互作用。通过光学显微镜和二次离子质谱进行的后期观察表明,Ca沿蛋白质纤维集中,并且晶体优先在纤维交叉上形成。我们证明,有组织的蛋白质与非结构化的蛋白质可以仅在纳米之间组装并在相同的环境中进行探测,在这种环境中,矿化被证明需要由细胞外基质的原纤维形成所施加的结构组织。

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