牡蠣蛋白片段對碳酸鈣礦化過程之影響

生物礦物為一種由無機物與有機分子組成的複合性材料，這些有機物通常為蛋白質或多醣類等生物分子。有趣的是此類生物分子可以精準地控制礦物的晶相與晶體成長的位置。但是因為缺乏一個好的研究系統，至今我們還不是非常了解生物中的有機分子如何去調控並引導晶體的生長。在本論文中我們建立了一個生物礦化的實驗系統，並由生物物理與晶體成長理論兩大角度切入進行研究。我們參考一種對於日本牡蠣珍珠層的成長相當重要的蛋白，依照其序列合成了一系列含有天門冬氨酸─天門冬氨酸─精氨酸─賴氨酸序列的胜肽。我們發現這些蛋白片段可以很專一地與文石這個碳酸鈣晶相進行結合，且胜肽的結合量與上述特殊序列的重複次數有著高度的相關性。而這些成功合成出來的胜肽─碳酸鈣仿生礦物可以使我們能夠更進一步地應用固態核磁共振光譜技術去研究有機與無機物的關係以及給予我們胜肽的結構訊息。此外我們也利用幾丁聚糖與牡蠣蛋白片段胜肽來模仿珍珠層的環境，使我們可以更進一步探討碳酸鈣在生物系統中可能的成長模式。我們發現片段胜肽的加入後，某些幾丁質模版的區域有較多數量的晶體形成，而這些晶體數目密度較高的區域中，文石的數量有著特別多的趨勢。以上結果使我們總結在胜肽分子與幾丁質的協同作用下，文石晶體成核的活化能可以被這些生物分子降低，因此引導了文石晶相的生成。本論文的研究與實驗系統對於碳酸鈣晶相的調控機制上有了更進一步的看法，我們相信後續的實驗將對於仿生材料的設計與開發會有重要的貢獻。

關鍵字

生物礦化；碳酸鈣；晶體成長理論；生物物理；固態核磁共振光譜；晶體成核

並列摘要

Biomineral is a composite material in organisms and it comprises an inorganic part as well as biomolecules like proteins and polysaccharides. These biomolecules can precisely control the crystal polymorphism and crystallization sites. However, the relationship between the two diverse organic and inorganic phases is still obscure and waiting to be explored because of lacking a good model system for study. In this thesis we have established a model system for investigating biomineralization process from the perspectives of biophysics and crystal-growth theory. Our model peptides were synthesized as motivated by the repeated sequence (DDRK) in Pif80, which is a crucial protein controlling the formation of the aragonitic nacreous layer in Pinctada fucata. We found that the Pif80 fragments can specifically associate with the aragonite phase of calcium carbonate and their binding propensity is highly dependent on the number of the repetition of DDRK sequence. These biomimetic peptide-mineral composites prepared here enable us to further utilize solid-state nuclear magnetic resonance to address the conformation of Pif80 peptides. In the view of crystal-growth theory, we employed β-chitin as a substrate with various Pif80 fragments to mimic the nacreous environment in order to investigate how biomolecules affect the crystallization of CaCO3 in nacre. Scanning electron microscopic analysis has shown that Pif80 peptides can induce the nucleation of aragonite on the β-chitin, which is distinct from the results without the substrate. Among the three peptides, Pif80-11 can increase the population densities of crystallites in the regions occupied by aragonite and we suspect this result is related to the higher binding affinity of Pif80-11. This binding effect probably reduces the energy barrier of nucleating aragonite and further induces the formation of aragonitic crystallites. We believe that the model system developed here can facilitate the future study in the mechanistic aspect of biomineralization that can be applied for material science.

並列關鍵字

biomineralization ； calcium carbonate ； crystal growth theory ； biophysics ； Pif80 protein ； solid-state nuclear magnetic resonance spectroscopy ； nucleation

參考文獻

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牡蠣蛋白片段對碳酸鈣礦化過程之影響

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