The mitogen-activated protein kinase (MAPK) p38α is a key regulator in many cellular processes, whose activity is tightly regulated by upstream kinases, phosphatases and other regulators. Transforming growth factor-β activated kinase 1 (TAK1) is an upstream kinase in p38α signaling, and its full activation requires a specific activator, the TAK1-binding protein (TAB1). TAB1 was also shown to be an inducer of p38α's autophosphorylation and/or a substrate driving the feedback control of p38α signaling. Here we determined the complex structure of the unphosphorylated p38α and a docking peptide of TAB1, which shows that the TAB1 peptide binds to the classical MAPK docking groove and induces long-range conformational changes on p38α. Our structural and biochemical analyses suggest that TAB1 is a reasonable substrate of p38α, yet the interaction between the docking peptide and p38α may not be sufficient to trigger trans-autophosphorylation of p38α.
The atypical PKC isoforms （ζ and t） play essential roles in regulating various cellular processes. Both the hetero-interaction between PKCζand p62 through their N-terminal PB 1 domains and the homo-oligomerization of p62 via its PB 1 domain are critical for the activation of NF-r.B signaling; however, the molecular mechanisms concerning the formation and regulation of these homotypic complexes remain unclear. Here we determined the crystal structure of PKCζ-PB 1 in complex with a mono- meric p62-PB 1 mutant, where the massive electrostatic interactions between the acidic OPCA motif of PKCζ-PB 1 and the basic surface of p62-PB 1, as well as additional hydrogen bonds, ensure the formation of a stable and specific complex. The PKCζ-p62 interaction is interfered with the modification of a specific Cys of PKCζ by the antiarthritis drug aurothiomalate, though all four cysteine residues in the PKCζ-PB 1 domain can be modified in in vitro assay. In addition, detailed structural and biochemical analyses demonstrate that the PB 1 domains of aPKCs belong to the type I group, which can depolymerize the high-molecular-weight p62 aggregates into homo-oligomers of lower order. These data together unravel the molecular mecha- nisms of the homo- or hetero-interactions between p62 and PKCζ and provide the basis for designing inhibitors of NF-r,.B sig- naling.
