Effect of C-terminal truncations on MLK7 catalytic activity and JNK activation

Abstract

Mixed lineage kinase 7 (MLK7) is a MAPKKK with enriched expression in heart and skeletal muscle that functions to activate JNK and p38. The MLKs have several conserved domains, including a leucine zipper that in other family members mediates oligomerization critical for catalytic activity and JNK activation. Nested C-terminal deletion mutants of MLK7 from 436 to 286 as well as a mutant lacking only the leucine zipper (delLZ) were generated to determine the role of these domains in catalytic activity and JNK activation. Specific activity of MLK7366 was 75% full length while 436, 322, and delLZ retained approximately 25% and 286, 4% of the full-length catalytic function, demonstrating that the leucine zipper, while not absolutely necessary for catalytic activity, is required to reach full catalytic function of the enzyme. Co-transfection studies of JNK with the MLK7 mutants demonstrated full JNK activation with MLK7, 436, and delLZ, marginal activation for 1–400 or 1–366, and no activation for 1–322, demonstrating that the leucine zipper is not required for JNK activation and that sequence contained in C-terminal residue 322–436 is necessary for full pathway activation by MLK7.