Residues Clustered in the Light-Sensing Knot of Phytochrome B are Necessary for Conformer-Specific Binding to Signaling Partner PIF3
A) Schematic of the N-terminal domain of Arabidopsis phyB (residues 1 to 651) showing the PAS (residues 103 to 219), GAF (residues 252 to 433), PHY (residues 444 to 623) and N-terminal extension (N) (residues 1 to 102) subdomains, as defined by sequence homology , and the locations of the missense mutations investigated here. Inverted triangle indicates chromophore attachment site (C357). B) Schematic representation of Deinococcus phytochrome structure adapted from Wagner et al. . Black arrows: β-strands. Black cylinders: α-helices. Grey labeling: positions of class I Arabidopsis phyB missense mutations. Red labeling – positions of class II Arabidopsis phyB missense mutations. Chromophore attachment site (C357) is indicated. Positions of mutated residues are indicated by red dots and were determined from the pairwise alignment of phyB with the Deinococcus phytochrome amino acid sequence. Blue box: “light-sensing knot”.