On Apr. 17, 2018, Xiaodong Liu‘s group published 'Improved calcium sensor GCaMP-X overcomes the calcium channel perturbations induced by the calmodulin in GCaMP' in Nature Communications.
GCaMP, one popular type of genetically-encoded Ca indicator, has been associated with various side-effects. Here we unveil the intrinsic problem prevailing over different versions and applications, showing that GCaMP containing CaM (calmodulin) interferes with both gating and signaling of L-type calcium channels (Ca 1). GCaMP acts as an impaired apoCaM and Ca /CaM, both critical to Ca 1, which disrupts Ca dynamics and gene expression. We then design and implement GCaMP-X, by incorporating an extra apoCaM-binding motif, effectively protecting Ca 1-dependent excitation–transcription coupling from perturbations. GCaMP-X resolves the problems of detrimental nuclear accumulation, acute and chronic Ca dysregulation, and aberrant transcription signaling and cell morphogenesis, while still demonstrating excellent Ca -sensing characteristics partly inherited from GCaMP. In summary, CaM/Ca 1 gating and signaling mechanisms are elucidated for GCaMP side-effects, while allowing the development of GCaMP-X to appropriately monitor cytosolic, submembrane or nuclear Ca , which is also expected to guide the future design of CaM-based molecular tools.