Enzymes efficiently catalyze numerous reactions, but re-engineering them to speed up reactions that are not known in nature is challenging. Lanthanides, particularly cerium complexes, have previously been used in photocatalytic transformations that proceed via radical species. However, these radical reactions are rarely stereoselective. In an effort to address this, Klein, Leiss-Maier et al. developed a lanthanide-binding enzyme by adding four glutamates in the center of a computationally designed protein scaffold. The resulting enzyme — which they called PhotoLanZyme 1.0 (PLZ1.0) — catalyzes radical C-C bond cleavage of 1,2-diols in the presence of cerium(III) chloride and visible light. To improve the photostability and metal binding kinetics, the team further engineered the photoenzyme by mutating tryptophans near the lanthanide binding site and introducing mutations to the protein surface to minimize unspecific cerium binding.

The final variant, PLZ1.4, could catalyze cleavage of several aromatic substituted diols in a diastereoselective manner, as well as cleavage of aromatic lignin model compounds. Using a fusion construct of PLZ1.1 with a Lpp–OmpA sequence (previously used for surface display of artificial metalloenzymes), the team established a whole-cell biocatalytic system for degradation of lignin model compounds in Escherichia coli. Finally, they demonstrated the applicability of natural lanthanide-dependent enzymes for cerium photoredox catalysis using alcohol dehydrogenase PedH from Pseudomonas putida KT2440, which requires the redox cofactor pyrroloquinoline quinone (PQQ) and a lanthanide ion for the reaction. The enzyme was expressed and reconstituted without PQQ. In the presence of cerium(III) chloride and light, PedH could catalyze diol cleavage. This study opens new avenues for engineering of artificial enzymes that can catalyze lanthanide-mediated photoredox reactions.

酶可以有效地催化许多反应，但重新设计它们以加速自然界中未知的反应是具有挑战性的。镧系元素，特别是铈络合物，以前已用于通过自由基物种进行的光催化转化。然而，这些自由基反应很少是立体选择性的。为了解决这个问题，Klein、Leiss-Maier 等人通过在计算设计的蛋白质支架的中心添加四种谷氨酸来开发一种镧系元素结合酶。所得酶——他们称之为 PhotoLanZyme 1.0 （PLZ1.0）——在氯化铈 （III） 和可见光存在下催化 1,2-二醇的自由基 C-C 键裂解。为了提高光稳定性和金属结合动力学，该团队通过突变镧系元素结合位点附近的色氨酸并将突变引入蛋白质表面以最大限度地减少非特异性铈结合来进一步改造光酶。

最后一种变体 PLZ1.4 可以非对映选择性方式催化几种芳香族取代二醇的裂解，以及芳香族木质素模型化合物的裂解。利用 PLZ1.1 与 Lpp-OmpA 序列（以前用于人工金属酶的表面显示）的融合构建体，该团队建立了一个全细胞生物催化系统，用于降解大肠杆菌中的木质素模型化合物。最后，他们证明了天然镧系元素依赖性酶使用来自恶臭假单胞菌 KT2440 的醇脱氢酶 PedH 进行铈光氧化还原催化的适用性，这需要氧化还原辅因子吡咯并喹啉醌 （PQQ） 和镧系元素离子进行反应。酶在没有 PQQ 的情况下表达和重构。在氯化铈 （III） 和光存在下，PedH 可以催化二醇裂解。这项研究为可以催化镧系元素介导的光氧化还原反应的人工酶的工程设计开辟了新的途径。