The Dual Characteristics of Light-Induced Cryptochrome 2, Homo-oligomerization and Heterodimerization, for Optogenetic Manipulation in Mammalian Cells

The photoreceptor cryptochrome 2 (CRY2) has become a powerful optogenetic tool that allows light-inducible manipulation of various signaling pathways and cellular processes in mammalian cells with high spatiotemporal precision and ease of application. However, it has also been shown that the behavior of CRY2 under blue light is complex, as the photoexcited CRY2 can both undergo homo-oligomerization and heterodimerization by binding to its dimerization partner CIB1. To better understand the light-induced CRY2 activities in mammalian cells, this article systematically characterizes CRY2 homo-oligomerization in different cellular compartments, as well as how CRY2 homo-oligomerization and heterodimerization activities affect each other. Quantitative analysis reveals that membrane-bound CRY2 has drastically enhanced oligomerization activity compared to that of its cytoplasmic form. While CRY2 homo-oligomerization and CRY2-CIB1 heterodimerization could happen concomitantly, the presence of certain CIB1 fusion proteins can suppress CRY2 homo-oligomerization. However, the homo-oligomerization of cytoplasmic CRY2 can be significantly intensified by its recruitment to the membrane via interaction with the membrane-bound CIB1. These results contribute to the understanding of the light-inducible CRY2-CRY2 and CRY2-CIB1 interaction systems and can be used as a guide to establish new strategies utilizing the dual optogenetic characteristics of CRY2 to probe cellular processes.