Backbone-cyclic proteins are of great scientific and therapeutic interest owing to their higher stability over their linear counterparts. Modification of such cyclic proteins at a selected site would further enhance their versatility. Here we report a chemoenzymatic strategy to engineer site-selectively modified cyclic proteins by combining butelase-mediated macrocyclization with the genetic code expansion methodology. Using this strategy, we prepared a cyclic protein which was modified with biotin or a cell-penetrating peptide at a genetically incorporated noncanonical amino acid, making the cyclization-stabilized protein further amenable for site-specific immobilization and intracellular delivery. Our results point to a new avenue to engineering novel cyclic proteins with improved physicochemical and pharmacological properties for potential applications in biotechnology and medicine.

中文翻译：

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固定和环状蛋白通过修饰遗传掺入的非天然氨基酸的细胞内传递。

骨环蛋白由于其相对于线性对应物的更高的稳定性而具有重大的科学和治疗意义。在选定位点修饰此类环状蛋白将进一步增强其多功能性。在这里，我们报告了一种化学酶策略，通过结合丁酸酶介导的大环化与遗传密码扩展方法来工程化位点选择性修饰的环状蛋白。使用这种策略，我们制备了一种环状蛋白质，该环状蛋白质在生物掺入的非规范氨基酸处被生物素或细胞穿透肽修饰，从而使环化稳定化蛋白质进一步适合于位点特异性固定和细胞内递送。