Fig. 5.

Critical interface contacts in an output loop between the fourth and fifth β-strands of PixD that undergoes significant movement upon light excitation. (A) Residues contributing to interface contacts are highlighted in red. Trp-91 is represented by a blue stick model and flavin by a yellow stick-sphere model. (B) The light signal induces the hydrogen-bond alteration around flavin, causing the flip of the Gln-50 side chain and the position switch between Trp-91 and Met-93. (C) Breaking the hydrogen bond between Trp-91 and Gln-50 transforms the light signal into the structural change around the Trp-91 (star) vicinity, including the loop that consists of the PixD dimer–dimer interface. As a result, the PixD decamer is broken into dimers and the PixD–PixE complex is disassembled.