Conformational analysis of the blue-light sensing protein YtvA reveals a competitive interface for LOV-LOV dimerization and interdomain interactions

The Bacillus subtilis protein YtvA is related to plant phototropins in that it senses UVA-blue-light by means of the flavin binding LOV domain, linked to a nucleotide-binding STAS domain. The structural basis for interdomain interactions and functional regulation are not known. Here we report the conformational analysis of three YtvA constructs, by means of size exclusion chromatography, circular dichroism (CD) and molecular docking simulations. The isolated YtvA-LOV domain (YLOV, aa 25-126) has a strong tendency to dimerize, prevented in full-length YtvA, but still observed in YLOV carrying the N-terminal extension (N-YLOV, aa 1-126). The analysis of CD data shows that both the N-terminal cap and the linker region (aa 127-147) between the LOV and the STAS domain are helical and that the central beta-scaffold is distorted in the LOV domains dimers. The involvement of the central beta-scaffold in dimerization is supported by docking simulation of the YLOV dimer and the importance of this region is highlighted by light-induced conformational changes, emerging from the CD data analysis. In YtvA, the beta-strand fraction is notably less distorted and distinct light-driven changes in the loops/turn fraction are detected. The data uncover a common surface for LOV-LOV and intraprotein interaction, involving the central beta-scaffold, and offer hints to investigate the molecular basis of light-activation and regulation in LOV proteins.