Time-Resolved X-Ray Solution Scattering Reveals the Structural Photoactivation of a Light-Oxygen-Voltage Photoreceptor

Abstract

Light-oxygen-voltage (LOV) receptors are sensory proteins controlling a wide range of organismal adaptations in multiple kingdoms of life. Because of their modular nature, LOV domains are also attractive for use as optogenetic actuators. A flavin chromophore absorbs blue light, forms a bond with a proximal cysteine residue, and induces changes in the surroundings. There is a gap of knowledge on how this initial signal is relayed further through the sensor to the effector module. To characterize these conformational changes, we apply time-resolved X-ray scattering to the homodimeric LOV domain from Bacillus subtilis YtvA. We observe a global structural change in the LOV dimer synchronous with the formation of the chromophore photoproduct state. Using molecular modeling, this change is identified as splaying apart and relative rotation of the two monomers, which leads to an increased separation at the anchoring site of the effector modules.

Signal transduction in photoreceptor histidine kinases

“…Due to the entangling of the A 0 α helices, complete dissociation of the LOV monomers is prevented. As recently demonstrated, [74][75][76] the weakening of the β-sheet:A 0 α interaction is rather channeled into a slight rotation and tilting apart of the monomers (Figure 3d). This quaternary transition entails a separation of the Jα anchor sites at the tips of the Iβ strands by around 3 Å which provides the mechanistic basis for signal propagation to the linker and the histidine kinase effector unit, see below.…”

“…The structural changes manifest within the LOV sensor after blue-light absorption in a single concerted step on the microsecond timescale, synchronously with thioadduct formation. Notably, consistent light-induced conformational transitions have been observed by two independent experimental techniques (double electron-electron resonance [DEER] 74 spectroscopy and X-ray solution scattering 75,76 ), and in the context of either the isolated BsYtvA photosensor or the composite LOV-SHK YF1. These findings not only confirm the observed signaling mode, but also they imply that this mode is little affected by C-terminal appendage of an effector module.…”

“…Although structural data of that type are not available yet, the conformational transitions that the YF1 SHK undergoes upon blue-light absorption were recently charted by EPR spectroscopy 74 and X-ray solution diffraction. 75,76 The time-resolved scattering data revealed a biphasic response of full-length YF1 to light absorption. A fast phase, rate-limited by photochemical events within the LOV photosensor, see above, occurs on the microsecond scale and is followed by a much slower phase on the millisecond scale.…”

“…To fully unravel signal‐dependent conformational transitions of the linker, one would ideally require atomically resolved structural information on the same SHK for different functional states. Although structural data of that type are not available yet, the conformational transitions that the YF1 SHK undergoes upon blue‐light absorption were recently charted by EPR spectroscopy and X‐ray solution diffraction . The time‐resolved scattering data revealed a biphasic response of full‐length YF1 to light absorption.…”

Signaltransduktion einer lichtregulierten Sensorhistidinkinase

“…S Mit paramagnetischer Elektronenresonanz-Spektroskopie (EPR) 12) und Röntgenbeugung (SAXS) 13 17,18) Zudem erlaubt die nun aufgeklärte Strukturänderung, den zugrundeliegenden LOV-Sensor als Baustein einzusetzen -damit lassen sich lichtregulierte Proteine konstruieren, die in der Optogenetik zum Einsatz kommen könnten. 19)…”