An evolutionarily conserved motif in the TAB1 C-terminal region is necessary for interaction with and activation of TAK1 MAPKKK

TAK1, a member of the MAPKKK family, is involved in the intracellular signa ling pathways mediated by transforming growth factor beta, interleukin 1, a nd Wnt, TAK1 kinase activity is specifically activated by the TAK1-binding protein TAB1. The C-terminal 68-amino acid sequence of TAB1 (TAB1-C68) is s ufficient for TAX1 interaction and activation Analysis of various truncated versions of TAB1-C68 defined a C-terminal 30-amino acid sequence (TAB1-C30 ) necessary for TAK1 binding and activation. NMR studies revealed that the TAB1-C30 region has a unique cu-helical structure. We identified a conserve d sequence motif, PYVDXA/TXF, in the C-terminal domain of mammalian TAB1, X enopus TAB1, and its Caenorhabditis elegans homolog TAP-I, suggesting that this motif constitutes a specific TAK1 docking site. Alanine substitution m utagenesis showed that, TAB1 Phe484, located in the conserved motif, is cru cial for TAK1 binding and activation. The C, elegans homolog of TAB1, TAP-1 , was able to interact with and activate the C. elegans homolog of TAK1, MO M-4. However, the site in TAP-1 corresponding to Phe-484 of TAB1 is an alan ine residue (Ala-364), and changing this residue to Phe abrogates the abili ty of TAP-1 to interact with and activate MOM-4. These results suggest that the Phe or Ala residue within the conserved motif of the TAB1-related prot eins is important for interaction with and activation of specific TAK1 MAPK KK family members in vivo.