Rational design of a stapled JAZ9 peptide inhibiting protein-protein interaction of a plant transcription factor

Coordinately regulated transcription factors EIN3/EIL1 and MYCs in ethylene and jasmonate signaling interact with the same domain of MED25

Ethylene (ET) and jasmonate (JA) are plant hormones that act synergistically to regulate plant development and defense against necrotrophic fungi infections, and antagonistically in response to wounds and apical hook formation. Previous studies revealed that the coordination of these responses is due to dynamic protein-protein interactions (PPI) between their master transcription factors (TFs) EIN3/EIL1 and MYC in ET and JA signaling, respectively. In addition, both TFs are activated via interactions with the same transcriptional mediator MED25, which upregulates downstream gene expression. Herein, we analyzed the PPI between EIN3/EIL1 and MED25, and as with the PPI between MYC3 and MED25, found that the short binding domain of MED25 (CMIDM) is also responsible for the interaction with EIN3/EIL1 - a finding which suggests that both TFs compete for binding with MED25. These results further inform our understanding of the coordination between the ET and JA regulatory systems.

Helical Foldamers and Stapled Peptides as New Modalities in Drug Discovery: Modulators of Protein-Protein Interactions

A “foldamer” is an artificial oligomeric molecule with a regular secondary or tertiary structure consisting of various building blocks. A “stapled peptide” is a peptide with stabilized secondary structures, in particular, helical structures by intramolecular covalent side-chain cross-linking. Helical foldamers and stapled peptides are potential drug candidates that can target protein-protein interactions because they enable multipoint molecular recognition, which is difficult to achieve with low-molecular-weight compounds. This mini-review describes a variety of peptide-based foldamers and stapled peptides with a view to their applications in drug discovery, including our recent progress.

Protein-protein interactions between jasmonate-related master regulator MYC and transcriptional mediator MED25 depend on a short binding domain

A network of protein–protein interactions (PPI) is involved in the activation of (+)-7-iso-jasmonoyl-L-isoleucine (JA-Ile), a plant hormone that regulates plant defense responses as well as plant growth and development. In the absence of JA-Ile, inhibitory protein jasmonate-ZIM-domain (JAZ) represses JA-related transcription factors, including a master regulator, MYC. In contrast, when JA-Ile accumulates in response to environmental stresses, PPI occurs between JAZ and the F-box protein COI1, which triggers JAZ degradation, resulting in derepressed MYC that can interact with the transcriptional mediator MED25 and upregulate JA-Ile-related gene expression. Activated JA signaling is eventually suppressed through the catabolism of JA-Ile and feedback suppression by JAZ splice variants containing a cryptic MYC-interacting domain (CMID). However, the detailed structural basis of some PPIs involved in JA-Ile signaling remains unclear. Herein, we analyzed PPI between MYC3 and MED25, focusing on the key interactions that activate the JA-Ile signaling pathway. Biochemical assays revealed that a short binding domain of MED25 (CMIDM) is responsible for the interaction with MYC, and that a bipartite interaction is critical for the formation of a stable complex. We also show the mode of interaction between MED25 and MYC is closely related to that of CMID and MYC. In addition, quantitative analyses on the binding of MYC3-JAZs and MYC3-MED25 revealed the order of binding affinity as JAZ^Jas < MED25^CMIDM < JAZ^CMID, suggesting a mechanism for how the transcriptional machinery causes activation and negative feedback regulation during jasmonate signaling. These results further illuminate the transcriptional machinery responsible for JA-Ile signaling.