Blue Flickers of Hope: Secondary Structure, Dynamics, and Putative Dimerization Interface of the Blue-Light Receptor YtvA from <i>Bacillus subtilis</i>

<i>Bacillus subtilis</i> is capable of responding to various kinds of extracellular, potentially harmful stimuli via a stress response pathway, which involves a signal transduction and integration hub, the stressosome, and finally leads to activation of σ<sup>B</sup>. One of the different signals initiating the underlying phosphorylation cascade is blue light. While it is known that the bacterial photoreceptor YtvA is responsible for blue light detection, the intramolecular activation mechanism and the structure of this multidomain protein are unknown. Using solution NMR spectroscopy, we have obtained a near complete backbone assignment of the full-length protein. More importantly, we report relaxation data and data on the solvent accessibility of full-length YtvA in the dark state which are interpreted with respect to secondary structure, the mobility, and the quaternary structure of the protein. Finally, we show that YtvA adopts an elongated domain orientation with LOV–LOV and STAS–STAS interactions on either side.