利用酵素與奈米微粒之生物分子交互作用調控催化活性

Abstract

蛋白質表面的修飾與辨識在生物科學領域裡常用來探討蛋白質與蛋白質交互作用及酵素催化活性，在本篇研究中，我們利用奈米微粒本身對生物分子的作用力將酵素修飾於粒子的表面並探討其酵素特性，我們發現酵素固定於奈米微粒上其活性會有顯著性的增加，利用動力學及熱力學實驗分析此具有酵素催化功能的奈米粒子，我們能夠解釋和預測其反應行為並了解此增強活性之機制。由於奈米微粒與生物分子的尺寸互相匹配，因此奈米粒子常用於酵素固定化之基材，在接下來的研究中，我們嘗試將酵素修飾於不同大小之奈米微粒，我們發現當固定於較小的粒子時，其反應速率明顯增強，經由進一步的動力學實驗發現，此奈米微粒的粒徑大小會影響此酵素與反應基質之親和力以至於改變其催化活性與行為。為了解釋奈米微粒在反應過程所扮演之角色，我們提出一套理論解釋此現象，由於不同大小之奈米微粒有不同的立體障礙效應，其碰撞機率會隨著粒徑變小而增加，因此對催化速率產生影響。本項研究包含了實驗數據以及理論探討，並詳細地解釋奈米粒子與酵素之間的交互作用，說明奈米微粒對於酵素催化行為所扮演的角色。在生物體中酵素活性的調控與生長、合成和代謝等反應直接相關，利用奈米微粒調控催化活性的能力對於日後在奈米生物領域上的發展有所貢獻。

Protein surface recognition provides an appealing tool to regulate protein–protein interactions and enzymatic activities in the field of biological science. We are interested in using nanoparticle (NP) to bind enzyme surfaces through multivalent interactions and then engineer the protein properties. In this study, we have investigated the activity of the enzyme–NP conjugates and demonstrated that adsorbing enzyme onto NPs significantly increased its enzymatic activity. We ascribe this event of the enzymatic reactions by kinetic and thermodynamic studies, which provide a way of understanding and predicting the catalytic behaviors of the enzyme-functionalized NPs. In addition, NPs are excellent systems for modeling enzymes’ surfaces because they can be readily fabricated on size scales comparable with those of their biomolecular targets. Therefore, we were curious to study whether varying the dimensions of the NPs would affect their catalytic reactions. We have developed a series of kinetic experiments to systematically analyze the NP size–dependent enzymatic activities, and have developed a model to explain the phenomenon. Kinetic studies revealed that association of enzyme with NPs did not influence the turnover number, but smaller NPs did promote the catalytic efficiency of enzyme by increasing its kinetic affinity. A shielding model, based on diffusion–collision theory, explains the correlation between the size effects and the kinetic responses of the enzyme–NP conjugates. This size-effect model provides chemical and physical meaning, leading to the observed substrate specificities and catalytic constants. From the combined kinetic and theoretical investigation of enzyme bound to NPs, we found that these conjugates acted as a controllable and efficient factor for modulating the activity of the enzyme. In nature, controllable modulation of enzyme activity is a potent means of regulating several cellular processes (e.g., signal transduction, biosynthesis, metabolism). The modulation of biocatalytic behavior is an attractive feature for exploitation in the field of nanobiotechnology.