The Amino-Terminal Helix Modulates Light-Activated Conformational Changes in AsLOV2

The mechanism of light-triggered conformational change and signaling in light-oxygen-voltage (LOV) domains remains elusive in spite of extensive investigation and their use in optogenetic studies. The LOV2 domain of Avenasativa phototropin 1 (AsLOV2), a member of the Per-Arnt-Sim (PAS) family, contains a flavin mononucleotide chromophore that forms a covalent bond with a cysteine upon illumination. This event leads to the release of the carboxy-terminal Jα helix, the biological output signal. Using mutational analysis, circular dichroism, and NMR, we find that the largely ignored amino-terminal helix is a control element in AsLOV2's light-activated conformational change. We further identify a direct amino-to-carboxy-terminal “input–output” signaling pathway. These findings provide a framework to rationalize the LOV domain architecture, as well as the signaling mechanisms in both isolated and tandem arrangements of PAS domains. This knowledge can be applied in engineering LOV-based photoswitches, opening up new design strategies and improving existing ones. [Display omitted] ► We investigate the mechanism of light-triggered conformational changes in AsLOV2. ► Spectroscopy indicates that the N-terminal helix unfolds upon illumination. ► This event triggers the unfolding of the C-terminal Jα helix. ► Results can be used in other LOV-based photoswitches and new designs strategies. ► An N- to C-terminal signaling mechanism is possible in other PAS domains.