GCaMP is one of the most widely used calcium indicators in neuronal imaging and
calcium cell biology. The newly developed GCaMP6 shows superior brightness and
ultrasensitivity to calcium concentration change. In this study, we determined
crystal structures of Ca(2+)-bound GCaMP6 monomer and dimer and presented
detailed structural analyses in comparison with its parent version GCaMP5G. Our
analyses reveal the structural basis for the outperformance of this newly
developed Ca(2+) indicator. Three substitution mutations and the resulting
changes of local structure and interaction explain the ultrasensitivity and
increased fluorescence intensity common to all three versions of GCaMP6. Each
particular substitution in the three GCaMP6 is also structurally consistent with
their differential sensitivity and intensity, maximizing the potential of using
GCaMP6 in solving diverse problems in neuronal research and calcium signaling.
Our studies shall also be beneficial to further structure-guided optimization of
GCaMP and facilitate the design of novel calcium indicators.
