Featured Article - July 2014
Short description: A chaperone–cochaperone interaction suppresses the JNK pathway and provides a novel target for pancreatic cancer drug discovery.
The DnaJ family of proteins are cochaperones to the DnaK/Hsp70 chaperones, which play multiple roles in stress response and protein quality control. DnaJ proteins bind to and enhance the ATPase hydrolysis activity of their DnaK partners. Knowledge of interactions between DnaK and DnaJ proteins may provide insight into downstream signaling events. In particular, as DnaK proteins are involved in apoptosis, there is a potential application for cancer intervention.
Powers and colleagues investigated the role of DnaJ in pancreatic cancer cells. Pancreatic cancer is associated with poor survival rates, and available therapies are rarely successful, pointing to the need for new drug development. The authors examined the human protein DnaJ homologue subfamily A member 1 (DNAJA1) and its role in the phosphorylation of c-Jun, a key transcription factor in the c-Jun N-terminal kinase (JNK) signaling pathway. Expression of DNAJA1 rendered pancreatic cancer cells more responsive to stress, as evidenced by reduced c-Jun phosphorylation. Since c-Jun is a phosphorylation substrate for JNK, the authors hypothesized that a DnaK–DnaJ complex may suppress JNK activity.
The authors determined the NMR solution structure of the J-domain of DNAJA1 (DNAJA1-JD). This domain adopts the expected J-domain fold and has a positively charged helix α2 connected to helix α3 by an extended loop containing the highly conserved histidine-proline-aspartate motif. A specific chaperone partner for DNAJA1 has not been identified, prompting the authors to use published NMR data on the interaction between the DnaJ J-domain and DnaK from Escherichia coli. Sequence alignment indicated that helix α2 DNAJA1-JD may participate in DnaK binding, in agreement with mutagenesis experiments. A subsequent NMR screen identified seven compounds that bind DNAJA1-JD specifically, all of which are negatively charged at physiological pH. Docking calculations indicate that the most active compound, O-phospho-L-serine, interacts with a binding pocket formed by residues in the loop region and helices α2 and α3. Although these ligands bind with relatively low affinity, this work provides chemical probes for future experiments and evidence for a druggable DNAJA1-JD surface.
J. L. Stark et al. Structure and function of human DnaJ homologue subfamily A member 1 (DNAJA1) and its relationship to pancreatic cancer.
Biochemistry 53, 1360-72 (2014). doi:10.1021/bi401329a