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

Abstract

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.

Blue‐Light Induced Interaction of LOV Domains from Chlamydomonas reinhardtii

“…This might happen because the distances between the lysines decrease in the photoexcited state so that the crosslinking reaction is more probable (see figure in the graphical abstract). Such a photoinduced increase of the LOV-LOV interaction might be important for signal transduction if, as suggested, [30] the autophosphorylation of phot is in fact a mutual cross-phosphorylation of a pair of phot proteins.…”

“…[23] The tendency of LOV domains to form dimers has been noticed previously. [25][26][27][28][29][30] Salomon et al showed by using size-exclusion chromatography that phot1-LOV1 dimerizes, but LOV2 stays monomeric. [25] In this work the authors suggested that LOV1 is responsible for phot dimerization, which would provide a possible functional role for the tandem organization of LOV domains in phot proteins.…”

“…These data led to the proposal of a common surface for LOV-LOV and intraprotein interaction that involves the central b scaffold. [30] Apparently, LOV-LOV interactions that lead to dimers are a common feature of many LOV domains, but their role in the signaling cascade still needs to be uncovered. In particular, it should be investigated whether this interaction is modulated by the photochemistry of the LOV domains.…”

“…[29] Recently, dimerization and interdomain interactions were observed in the isolated YtvA-LOV domain by size-exclusion chromatography. [30] Circular dichroism (CD) spectroscopy measurements showed a central distortion in the b scaffold of the LOV domain. These data led to the proposal of a common surface for LOV-LOV and intraprotein interaction that involves the central b scaffold.…”

Shedding (blue) light on algal gene expression

“…In the crystal structure of YtvA-LOV, the linker instead protrudes outside of the LOV core, and the ␤-scaffold is engaged in the tight LOV-LOV dimer (20). In full-length YtvA, the ␤-scaffold is involved in intraprotein/interdomain interactions, and there is no light-induced unfolding of the linker, whose exact orientation remains to be determined (21).…”