Fig. 1: High resolution 3D structure of the PSM from the P. syringae (Ps) BphP1 dimer as Pr.

a Domain organization of PsBphP1. Shown are the positions of BV, the PAS, GAF, and PHY domains, and the NTE, knot lasso (KL) and hairpin (HP) features, portions of the S-helix linker, and the DHp and CA domains within the HK bidomain of the OPM. The numbers delineate domain boundaries within the polypeptide. Cys16, which forms a thioether linkage with BV is identified by the red circle. His530, which provides the phosphoacceptor site in the DHp, is indicated by the arrow. The length of the NTE was extended for clarity. b Relative positions of BV as Pr in the PsBphP1 dimer (PDB 8U4X) with that determined previously by X-ray crystallography of a PSM fragment from D. radiodurans (Dr) BphP (PDB 4Q0J²⁹). The nitrogen, oxygen, and sulfur atoms are in blue, red, and yellow, respectively. The A-D pyrrole rings are labeled. The 3² carbon that forms the thioether linkage with the apoprotein and the 18² vinyl carbon are labeled for reference. c Cryo-EM model of the BV-binding pocket from the A protomer (sticks) of PsBphP1 superposed with the EM map (gray mesh). BV and the NTE, GAF domain, and PHY hairpin carbon atoms are in cyan, black, green, and orange, respectively. d Surface-rendered 2.8-Å resolution view of the 3D EM map of the dimeric PsBphP1 PSM. EM density was rendered at 5 σ. EM density within 3 Å of a modeled atom was color-coded by domain with NTE, PAS, GAF, PHY, S helix, and BV colored in black, blue, green, yellow/orange, teal/light cyan, and red, respectively; those at greater distances were rendered white. Positions of the helical spines (HS), HP, NTE, and KL features are highlighted. Dimensions of the dimeric PSM are indicated where the width excludes NTE and hairpin contributions. e Orthogonal cartoon views of the dimeric PSM model of PsBphP1 as Pr. Features are colored as in panel (d). BV is shown in red sticks. C, C-terminus.