Optical Control of the Ca²⁺ Concentration in a Live Specimen with a Genetically Encoded Ca²⁺-Releasing Molecular Tool

Calcium ion (Ca²⁺) is an important second messenger implicated in the control of many different cellular processes in living organisms. Ca²⁺ is typically studied by direct visualization using chemically or genetically encoded indicators. A complementary, and perhaps more useful, approach involves direct manipulation of Ca²⁺ concentration; tools for this exist but are rather poorly developed compared to the indicators at least. Here, we report a photoactivatable Ca²⁺-releasing protein, photoactivatable Ca²⁺ releaser (PACR), made by the insertion of a photosensitive protein domain (LOV2) into a Ca²⁺ binding protein (calmodulin fused with the M13 peptide). As the PACR is genetically encoded, and unlike conventional optical control tools (e.g., channel rhodopsin) not membrane bound, we are able to restrict expression within the cell, to allow subcellular perturbation of Ca²⁺ levels. In whole animals, we are able to control the behavior of Caenorhabditis elegans with light by expressing the PACR only in the touch neuron.