Fig. 1: Structure of the apo-form of PRT1^ZZ.

a Structure of the apo-form of PRT1^ZZ in a ribbon diagram. Three loops (1: red, 2: purple, and 3: green) are indicated and labeled. Key residues for N-degron recognition are drawn using a stick model with labels. N* and C* denote the first and last residues of the construct. Bound zinc atoms (Zn1 and Zn2) are shown as gray balls. The estimated position of F352 is represented by the transparent stick model (invisible phenyl side chain in apo structure). b Transparent molecular surface of apo-form ZZ domain representing electrostatic potential. Red and blue colors represent negatively and positively charged areas, respectively. The N-degron binding pocket is highlighted as a red circle. c Topology diagram of PRT1^ZZ. The ZZ domain of PRT1 has a conserved ZZ domain topology. The construction comprises three β-sheets and one α-helix. The loops (L1–L3) containing the key residues are represented with the same colors as those in (a). d Schematic diagram showing Zn ion coordination of PRT1^ZZ. Zn1 and Zn2 ions coordinate with C₄ and C₂H₂ Zn-finger motifs, respectively.