Mitogen activated protein kinases (MAPKs) are key signaling enzymes that are activated by phosphorylation of a TXY motif in their activation loops. While dual-specificity MAPK kinases activate many MAPKs (canonical signaling), atypical kinases and autophosphorylation can also activate MAPKs (non-canonical signaling). A great deal is known about the role of canonical signaling pathways in health and disease. Much less is known about non-canonical signaling. Smk1 is a meiosis- specific MAPK in the yeast S. cerevisiae that controls gamete formation (sporulation) through a non-canonical signaling pathway that generates different forms of the MAPK at different stages of meiosis. First, the CDK activating kinase, Cak1, phosphorylates Smk1's activating T-residue as the meiotic divisions are taking place. This monophosphorylated form of Smk1 is distributed throughout the cell. Later in the program (at anaphase II), a meiosis-specific protein, Ssp2, binds to Smk1 and activates the cis-autophosphorylation of its Y-residue. This reaction occurs at specific membraneous structures that cellularize the haploids generated in this specialized cell division. Thus, Ssp2 delivers a pulse of the doubly phosphorylated MAPK to the ?right place? at the ?right time? in this developmental program. This spatiotemporal specificity is achieved by modularity of the Ssp2 protein; it is localized by a targeting domain (TD) and it activates cis-autophosphorylation of the MAPK via a kinase activating domain (KAD). The Ssp2KAD is itself composed of segments that bind Smk1 and a regulatory RNA recognition motif (RRM). This proposal is to use the Ssp2KAD/Smk1 reaction as a model to study autoactivation of MAPKs in the context of a developmental system.
The specific aims of this proposal are: 1- Elucidate molecular mechanisms of non-canonical MAPK signaling using a bacterial reconstitution system and purified proteins, 2-Test a competition-based switch-site model for Smk1 activation, and 3- Identify the RNA(s) recognized by the RNA recognition motif in Ssp2.
Mitogen activated protein kinases (MAPKs) are key regulators of cell growth, differentiation, and apoptosis, that are dysregulated in a variety of diseases/disorders ranging from birth defects to cancer, to Alzheimer's disease. This project will use yeast as a model system to study MAPK autoactivation, a poorly understood regulatory mechanism that activates MAPKs, and MAPK-like kinases. The proposed studies will generate new insights into mechanisms that control MAPK signaling that impact health and disease.
| Omerza, Gregory; Tio, Chong Wai; Philips, Timothy et al. (2018) The meiosis-specific Cdc20 family-member Ama1 promotes binding of the Ssp2 activator to the Smk1 MAP kinase. Mol Biol Cell 29:66-74 |
| Tio, Chong Wai; Omerza, Gregory; Phillips, Timothy et al. (2017) Ssp2 Binding Activates the Smk1 Mitogen-Activated Protein Kinase. Mol Cell Biol 37: |
