Potential Activation Mechanism of Calcium Indicator WHaloCaMP1a Revealed by the Crystal Structure and Molecular Dynamics Simulations

Chemigenetic indicators combined with advanced organic fluorophores have become increasingly popular in biosensor development due to their integration of protein biocompatibility and the superior optical properties of dyes. However, despite the development of various biosensors based on these systems, the underlying activation mechanisms remain obscure. Here, we report the first crystal structure of the recently developed calcium indicator WHaloCaMP1a in complex with the rhodamine-based fluorophore BD566HTL. Integrating structural analysis with molecular dynamics simulations, we identify a potential activation mechanism of WHaloCaMP1a and reveal novel interactions between the sensor and BD566. These findings provide new insights for the rational design of biosensors and the study of protein–dye coevolution.