The ability to programme new modes of catalysis into proteins would allow the development of enzyme families with functions beyond those found in nature. To this end, genetic code expansion methodology holds particular promise, as it allows the site-selective introduction of new functional elements into proteins as non-canonical amino acid side chains.^1-4 Here, we exploit an expanded genetic code to develop a photoenzyme that operates via triplet energy transfer catalysis, a versatile mode of reactivity in organic synthesis that is currently not accessible to biocatalysis.^5-12 Installation of a genetically encoded photosensitiser into the beta-propeller scaffold of DA_20_00¹³ converts a de novo Diels-Alderase into a photoenzyme for [2+2]-cycloadditions (EnT1.0). Subsequent development and implementation of a platform for photoenzyme evolution afforded an efficient and enantioselective enzyme (EnT1.3, up to 99% e.e.) that can promote intramolecular and bimolecular cycloadditions, including transformations that have proven challenging to achieve selectively with small molecule catalysts. EnT1.3 performs >300 turnovers and, in contrast to small molecule photocatalysts, can operate effectively under aerobic conditions and at ambient temperatures. An X-ray crystal structure of an EnT1.3-product complex shows how multiple functional components work in synergy to promote efficient and selective photocatalysis. This study opens up a wealth of new excited-state chemistry in protein active sites and establishes the framework for developing a new generation of enantioselective photocatalysts.

将新的催化模式编程到蛋白质中的能力将允许开发具有超出自然界中发现的功能的酶家族。为此，遗传密码扩展方法具有特别的前景，因为它允许将新的功能元件作为非规范氨基酸侧链选择性地引入蛋白质中。 ^1-4在这里，我们利用扩展的遗传密码来开发一种通过三重态能量转移催化发挥作用的光酶，这是有机合成中的一种多功能反应模式，目前生物催化无法实现。 ^5-12将基因编码的光敏剂安装到 DA_20_00 ¹³的 β 螺旋桨支架中，将de novo Diels-Alderase 转化为用于 [2+2]-环加成的光酶 (EnT1.0)。随后光酶进化平台的开发和实施提供了一种高效的对映选择性酶（EnT1.3，高达 99% ee ），可以促进分子内和双分子环加成，包括已证明用小分子催化剂选择性实现具有挑战性的转化。 EnT1.3 的转换次数超过 300 次，与小分子光催化剂相比，它可以在有氧条件和环境温度下有效运行。 EnT1.3-产物复合物的 X 射线晶体结构显示了多个功能成分如何协同作用以促进高效和选择性的光催化。这项研究在蛋白质活性位点开辟了丰富的新激发态化学，并建立了开发新一代对映选择性光催化剂的框架。