Determinants That Control The Specific Interactions Between TAB1 And P38α

Intracellular signal transduction pathways regulate cellular responses to physiological and nonphysiological stimuli. The mitogen-activated protein kinases (MAPKs) play an important role in a variety of biological processes. MAPK kinases are in turn activated by phosphorylation by the MAPK kinase kinases (MAPKKKs). Ge et al.(2002) showed that there is another way to activate the so-called stress-activated MAPK known as p38α. They have revealed that TAB1 interacts with p38αand induces p38αautophosphorylation. Therefore, the determination of binding sequence of TAB1 and p38αis critical for us to know the interesting protein-protein interaction between them.Here, we examined the sequence requirements in TAB1 and p38αthat drive their interaction. Deletion and point mutations in TAB1 reveal that a proline residue in the C terminus of TAB1 (Pro412) is necessary for its interaction with p38α. Furthermore, a cryptic D-domain like docking site was identified adjacent to the N terminus of Pro412, putting Pro412 in theΦB+3 position of the docking site. Through mutational analysis, we found that the previously identified hydrophobic docking groove in p38αis involved in this interaction, whereas the CD domain and ED site are not. Furthermore, chimeric analysis using TAB1 non-binding p38β, revealed a previously unidentified locus of p38αcomprising Thr218 and Ile275 that is essential for specific binding of p38αto TAB1. Converting either of these residues to the corresponding amino acid of p38βabolishes p38αinteraction with TAB1. Adjacent to Thr218 and Ile275 is a site where large conformational changes occur in the presence of docking-site peptides derived from p38αsubstrates and activators. The results suggest that TAB1-induced autophosphorylation of p38αresults from conformational changes that are similar but unique to those seen in p38αinteractions with its substrates and activating kinases.