TRPswitchA Step-Function Chemo-optogenetic Ligand for the Vertebrate TRPA1 Channel

Chemo-optogenetics has produced powerful
tools for optical control
of cell activity, but current tools suffer from a variety of limitations
including low unitary conductance, the need to modify the target channel,
or the inability to control both on and off switching. Using a zebrafish
behavior-based screening strategy, we discovered “TRPswitch”,
a photoswitchable nonelectrophilic ligand scaffold for the transient
receptor potential ankyrin 1 (TRPA1) channel. TRPA1 exhibits high
unitary channel conductance, making it an ideal target for chemo-optogenetic
tool development. Key molecular determinants for the activity of TRPswitch
were elucidated and allowed for replacement of the TRPswitch azobenzene
with a next-generation azoheteroarene. The TRPswitch compounds enable
reversible, repeatable, and nearly quantitative light-induced activation
and deactivation of the vertebrate TRPA1 channel with violet and green
light, respectively. The utility of TRPswitch compounds was demonstrated
in larval zebrafish hearts exogenously expressing zebrafish Trpa1b,
where the heartbeat could be controlled using TRPswitch and light.
Therefore, TRPA1/TRPswitch represents a novel step-function chemo-optogenetic
system with a unique combination of high conductance, high efficiency,
activity against an unmodified vertebrate channel, and capacity for
bidirectional optical switching. This chemo-optogenetic system will
be particularly applicable in systems where a large depolarization
current is needed or sustained channel activation is desirable.