The design of synthetic optogenetic tools that allow precise spatiotemporal
control of biological processes previously inaccessible to optogenetic control
has developed rapidly over the last years. Rational design of such tools
requires detailed knowledge of allosteric light signaling in natural
photoreceptors. To understand allosteric communication between sensor and
effector domains, characterization of all relevant signaling states is required.
Here, we describe the mechanism of light-dependent DNA binding of the
light-oxygen-voltage (LOV) transcription factor Aureochrome 1a from
Phaeodactylum tricornutum (PtAu1a) and present crystal structures of a dark
state LOV monomer and a fully light-adapted LOV dimer. In combination with
hydrogen/deuterium-exchange, solution scattering data and DNA-binding
experiments, our studies reveal a light-sensitive interaction between the LOV
and basic region leucine zipper DNA-binding domain that together with LOV
dimerization results in modulation of the DNA affinity of PtAu1a. We discuss the
implications of these results for the design of synthetic LOV-based photosensors
with application in optogenetics.
