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Figure 8
Observation of slow protein dynamics in LOV2 leading to complex C-terminus reordering concomitant with loss of crystal symmetry. (a) Structural description of the events occurring to the LOV2 C-terminus along the illumination sequence described in Fig. 1[link](b). The 2FobsFcalc electron density map contoured at a 1.5σ level is superimposed on the C-terminus (residues 491 to 503) and on residue W467 for the ground state, then at selected time points between the between the PS equilibrium (t < 0 s) and 1620 s. The C-terminus is ordered in the D-state, disorders in the PS equilibrium, then progressively reorders until a crystal phase transition at ∼70 s, at which point each monomer in the asymmetric unit of the new space group orders dissimilarly. One monomer quickly reorders as in the D-state, the other orders more slowly to a distinct, hook-shaped conformation. The phase transition is governed by a flipping of a conserved tryptophan residue positioned in the vicinity of the C-terminus. The resulting photocycle cannot proceed back to the D-state (red cross), but can be reset by re-illumination. (b) Illustration of C-terminus disordering/ordering by monitoring of the normalized B-factor of the stretch of residues 493 to 495 for monomer A (α-helical C-terminus) in orange, and for monomer B (hook-shaped C-terminus) in blue. (c) Corresponding evolution of the normalized B-factor of W467, suggesting a rationale for space group transition.

Volume 9| Part 6| November 2022| Pages 756-767
ISSN: 2052-2525