Fig. 6: The YΦ motif model for terminus-dependent h20S activation.
From: The YΦ motif defines the structure-activity relationships of human 20S proteasome activators
a Model summarizing the major features of the HbYX motif, for comparison. b Model of the nYΦn (YΦ) motif summarizes the proposed mechanism for termini-mediated activation of the h20S. The critical interactions (red) include polar contacts (squiggle) between Tyr residues and αGlu25 and αGly19 and π stacking between the Tyr residues (dotted line). The carboxylate interaction with αLys66 is also important. Secondary interactions (pink) are denoted for the P1 (orange), P2 (blue), P3 (green), and P4 (purple) residues. In addition, the P5 and P6 are likely to play a role. Note that multivalency seems to allow PAs to, in some cases, overcome a subset of these requirements.
