Scientists have developed a new light-sensitive, plant–human hybrid protein molecule, OptoSTIM1, that can efficiently modulate calcium channels and was shown to improve learning capacity in mice. The South Korean researchers, whose work was published in Nature Biotechnology [Kyung et al. Nat. Biotechnol. (2015) DOI: 10.1038/nbt.3350], were able to refine the process for precision control of cellular calcium (Ca2+) channels in living organisms with their new molecule.
Using optogenetics, a technique that involves using light to control cells in living tissue, the team used a photoreceptor protein called cryptochrome 2 (Cry2) taken from a small, flowering plant called Arabidopsis thaliana, before combining it with the STromal Interaction Molecule 1 (STIM1), a protein present in nearly all animals. This opens cellular Ca2+ channels, resulting in the hybrid molecule.
On introducing a blue light to the OptoSTIM1 expressing cells, they could coax them to open their Ca2+ channels and let in an influx of calcium ions from outside the cell. The levels of Ca2+ that cells took up was greater than previous attempts since the OptoSTIM1 was more efficient than previous optogenetic molecules, and Cry2 has an affinity for clustering under blue light. As researcher Taeyoon Kyung said, “Our method worked better because other plant proteins are not as efficient as Cry2 at clustering”.
For living cells, they expressed zebrafish embryos with OptoSTIM1; once the expressing cells had been exposed to the blue light, they showed signs of Ca2+ uptake, while the others did not. They then looked at intercellular Ca2+ signaling by testing human embryonic stem cells by exposing blue light to only a single cell in a colony that expressed OptoSTIM1. Although only one cell was illuminated with blue light, they were able to identify a Ca2+ delayed response in other (non-illuminated) cells that were further away, so there must be some sort of intercellular communication.
For OptoSTIM1 in the hippocampus of a living mouse, to gain insight into the functional effect of the Ca2+ influx, sets of light-illuminated and non-illuminated mice expressing OptoSTIM1 were compared while introducing a conditioning cue and a fear stimulus. It was found that the former had more of a fear response memory when being tested without the conditioning cue than the non-light-stimulated mice, indicating that the OptoSTIM1 expression (and resultant Ca2+ uptake) was an effective method for memory enhancement.
The study could lead to new research into optogenetically enhanced memory and learning, while those neurological diseases that spring from a dysfunction in Ca2+ regulation (including Alzheimer’s) could be influenced by controlling the Ca2+ channels in the brain to help identify applications for drugs.
“Our method worked better because other plant proteins are not as efficient as Cry2 at clustering”Taeyoon Kyung