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. 2013 Sep 13;8(9):e74518. doi: 10.1371/journal.pone.0074518

Figure 1. Scheme of substrate translocation from the GRL to the MPP active site.

Figure 1

Panel A shows the overall structure of MPP. The van der Waals surface of α-MPP and β-MPP subunits and GRL is in yellow, orange and green, respectively. Panel B shows the conformation and position of the substrate during its recognition by the α-MPP GRL (GRL-bound structure; red tube) and just prior to its subsequent proteolysis in MPP active site (AS-bound structure; pink tube). The direction of substrate translocation between these two boundary positions is indicated by blue arrow. In the GRL-bound structure residue F10 contributes to the hydrophobic interaction with GRL and residue R8 (i.e. the R-2 motif) is exposed to the β-MPP subunit. In the AS-bound structure the substrate is bound in an extended conformation and its R8 residue interacts with the R-2-binding motif. The zinc-binding motif and R-2-binding motif are shown schematically as cyan and orange spheres which correspond to the zinc-ion and residues E160 and D164 residues of the β-MPP subunit. The distances between the substrate R8 residue and the R-2-binding motif in the GRL-bound and AS-bound structure are shown as dashed black lines.