Steric Interactions at Gln154 in ZEITLUPE Induce Reorganization of the LOV Domain Dimer Interface

Plants measure light, quality, intensity, and duration to coordinate growth and development with daily and seasonal changes in environmental conditions, however, the molecular details linking photochemistry to signal transduction remain incomplete. Two closely related Light, Oxygen, or Voltage (LOV) domain containing photoreceptor proteins ZEITLUPE (ZTL) and FLAVIN-BINDING, KELCH REPEAT, F-BOX 1 (FKF1) divergently regulate the protein stability of circadian clock and photoperiodic flowering components to mediate daily and seasonal development. Using structural approaches, we identified that mutations at the Gly46 position led to global rearrangements of the ZTL dimer interface. Specifically, introduction of G46S and G46A variants that mimic equivalent residues found in FKF1 induce a 180{degrees} rotation about the dimer interface that is coupled to ordering of N- and C-terminal signaling elements. These conformational changes hinge upon rotation of a C-terminal Gln residue analogous to that present in light-state structures of ZTL. The results presented herein, confirm a divergent signaling mechanism within ZTL that deviates from other members of the LOV superfamily and suggests that mechanisms of signal transduction in LOV proteins may be fluid across the LOV protein family.