Site-Specific Bioconjugation of an Organometallic Electron Mediator to an Enzyme with Retained Photocatalytic Cofactor Regenerating Capacity and Enzymatic Activity
作者:Sung Lim、Sungho Yoon、Yong Kim、Inchan Kwon
DOI:10.3390/molecules20045975
日期:——
Photosynthesis consists of a series of reactions catalyzed by redox enzymes to synthesize carbohydrates using solar energy. In order to take the advantage of solar energy, many researchers have investigated artificial photosynthesis systems mimicking the natural photosynthetic enzymatic redox reactions. These redox reactions usually require cofactors, which due to their high cost become a key issue when constructing an artificial photosynthesis system. Combining a photosensitizer and an Rh-based electron mediator (RhM) has been shown to photocatalytically regenerate cofactors. However, maintaining the high concentration of cofactors available for efficient enzymatic reactions requires a high concentration of the expensive RhM; making this process cost prohibitive. We hypothesized that conjugation of an electron mediator to a redox enzyme will reduce the amount of electron mediators necessary for efficient enzymatic reactions. This is due to photocatalytically regenerated NAD(P)H being readily available to a redox enzyme, when the local NAD(P)H concentration near the enzyme becomes higher. However, conventional random conjugation of RhM to a redox enzyme will likely lead to a substantial loss of cofactor regenerating capacity and enzymatic activity. In order to avoid this issue, we investigated whether bioconjugation of RhM to a permissive site of a redox enzyme retains cofactor regenerating capacity and enzymatic activity. As a model system, a RhM was conjugated to a redox enzyme, formate dehydrogenase obtained from Thiobacillus sp. KNK65MA (TsFDH). A RhM-containing azide group was site-specifically conjugated to p-azidophenylalanine introduced to a permissive site of TsFDH via a bioorthogonal strain-promoted azide-alkyne cycloaddition and an appropriate linker. The TsFDH-RhM conjugate exhibited retained cofactor regenerating capacity and enzymatic activity.
光合作用由氧化还原酶催化的一系列反应组成,利用太阳能合成碳水化合物。为了利用太阳能,许多研究人员研究了模仿自然光合作用酶氧化还原反应的人工光合作用系统。这些氧化还原反应通常需要辅助因子,而辅助因子成本高昂,成为构建人工光合作用系统的关键问题。研究表明,将光敏剂和基于 Rh 的电子介质(RhM)结合起来,可以光催化再生辅助因子。然而,要维持高效酶促反应所需的高浓度辅因子,就需要高浓度的昂贵的 RhM;这使得这一过程的成本过高。我们假设,将电子介质与氧化还原酶结合,可以减少高效酶促反应所需的电子介质数量。这是因为当氧化还原酶附近的局部 NAD(P)H 浓度变高时,光催化再生的 NAD(P)H 就很容易被氧化还原酶利用。然而,RhM 与氧化还原酶的传统随机共轭可能会导致辅因子再生能力和酶活性的大量丧失。为了避免这一问题,我们研究了将 RhM 与氧化还原酶的允许位点生物共轭是否能保持辅因子再生能力和酶活性。作为一个模型系统,RhM 与一种氧化还原酶--从硫杆菌 KNK65MA(TsFDH)中获得的甲酸脱氢酶--共轭。通过生物正交菌株促进的叠氮-炔烃环加成和适当的连接剂,将含有叠氮基团的 RhM 与对-叠氮苯丙氨酸特异性地连接到 TsFDH 的允许位点上。 TsFDH-RhM 共轭物保留了辅助因子再生能力和酶活性。