Characterization of a microtubule‐associated protein, doublecortin (DCX), as a substrate of c‐Jun N‐terminal Kinases (JNKs)

We are interested how docking motifs contribute to substrate recognition by JNK, a Ser/Thr protein kinase and member of the Mitogen‐Activated Protein Kinase (MAPK) family. The activation of JNK signaling pathways and concomitant phosphorylation of a range of JNK substrates has been implicated with regulation of critical events, including cell growth and proliferation, cell division and cell death. Specifically, we are defining the structural and functional properties of the microtubule‐associated protein doublecortin (DCX) as a JNK substrate. DCX is unusual with its evolutionary conserved DC domains, rather than a typical linear basic/hydrophobic motif, reported to mediate its interaction with JNK. Using mass spectrometry, we have identified a novel JNK‐mediated phosphorylation site in the DCX protein, and confirmed the phosphorylation of this site by mutagenesis and detection by phosphospecific antibodies. Through our use of NMR approaches, we are gaining new structural insights into DCX with the ultimate aim to identify the features of the JNK‐DC domain interaction interface that support this non‐conventional mode of JNK‐substrate recognition.