Fig. 5: Detailed conformational changes and a model for Pr→Pfr photoconversion of full-length PsBphP1.

a Straightening the GAF-PHY helical spine kink centered at Thr326 during photoconversion shown by orthogonal views of the Pr (blue) and Pfr (DoD) (yellow) cartoon models. b Rotation of the PHY domain enforced by the β-stranded to α-helical transition of the hairpin shown by orthogonal views of the Pr (blue) and Pfr(DoD) (yellow) cartoon models superposed via the GAF domains. c Light-induced pivot of the helical spine exiting the GAF domain around Val-307. GAF domains of protomer A were superposed for Pr, Pfr (DoD), Pfr (medial), and Pfr (splayed) models of PsBphP1. (left) Cartoon models positioning the helical spine in protomer A. (right) Cartoon models highlighting the positions of the helical spine in protomers B after superposition of the GAF domain of protomers A. The positions of Ala72 highlight the range of motion for the PAS-GAF domain. d Orthogonal cartoon views of the dimer as Pr. Domains/features are colored as in Fig. 1d. e Orthogonal cartoon views of Pfr illustrating movements within the PsBphP1 dimer upon photoconversion. Include are: (i) tugging of the hairpin closer to the GAF domain as the hairpin converts from an anti-parallel β-strand to α-helical, (ii) rotation of the PHY domains with coincident straightening of the helical spine, (iii) pivoting of the GAF domains around V307; (iv) movement of the GAF-PHY helical spines closer to each other (red arrow), and (v) scissoring of the sister S-helices. f Close-up view of the proposed positions of the CA domain as Pr and Pfr showing downward movement and rotation of the ATP-binding pocket closer to His530 (vi). The Pr and Pfr images were derived from the protomer A models described in Figs. 2c and 4. Dashed orange ovals identify the ATP-binding pocket.