Molecular switches alterable between two stable states by environmental stimuli, such as light and temperature, offer the potential for controlling biological functions. Here, we report a circular photoswitchable protein complex made of multiple protein molecules that can rapidly and reversibly switch with significant conformational changes. The structural and photochromic properties of photoactive yellow protein (PYP) are harnessed to construct circular oligomer PYPs (coPYPs) of desired sizes. Considering the light-induced N-terminal protrusion of monomer PYP, we expected coPYPs would expand upon irradiation, but time-resolved X-ray scattering data reveal that the late intermediate has a pronounced light-induced contraction motion. This work not only provides an approach to engineering a novel protein-based molecular switch based on circular oligomers of well-known protein units but also demonstrates the importance of characterizing the structural dynamics of designed molecular switches.

通过环境刺激（例如光和温度）可在两种稳定状态之间改变的分子开关提供了控制生物功能的潜力。在这里，我们报道了一种由多个蛋白质分子组成的圆形光开关蛋白质复合物，它可以快速、可逆地开关并产生显着的构象变化。利用光活性黄色蛋白 (PYP) 的结构和光致变色特性构建所需大小的环状低聚物 PYP (coPYP)。考虑到单体 PYP 的光诱导 N 端突出，我们预计 coPYP 在照射后会膨胀，但时间分辨 X 射线散射数据显示，后期中间体具有明显的光诱导收缩运动。这项工作不仅提供了一种基于众所周知的蛋白质单元的环状低聚物设计新型蛋白质分子开关的方法，而且还证明了表征所设计的分子开关的结构动力学的重要性。