Conformational Control of the Ste5 Scaffold Protein Insulates Against MAP Kinase Misactivation

Department of Cellular and Molecular Pharmacology, University of California, San Francisco, 600 16th Street, San Francisco, CA 94158, USA.
Science (Impact Factor: 33.61). 08/2012; 337(6099):1218-22. DOI: 10.1126/science.1220683
Source: PubMed


Cells reuse signaling proteins in multiple pathways, raising the potential for improper cross talk. Scaffold proteins are thought to insulate against such miscommunication by sequestering proteins into distinct physical complexes. We show that the scaffold protein Ste5, which organizes the yeast mating mitogen-activated protein kinase (MAPK) pathway, does not use sequestration to prevent misactivation of the mating response. Instead, Ste5 appears to use a conformation mechanism: Under basal conditions, an intramolecular interaction of the pleckstrin homology (PH) domain with the von Willebrand type A (VWA) domain blocks the ability to coactivate the mating-specific MAPK Fus3. Pheromone-induced membrane binding of Ste5 triggers release of this autoinhibition. Thus, in addition to serving as a conduit guiding kinase communication, Ste5 directly receives input information to decide if and when signal can be transmitted to mating output.

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Available from: Scott Coyle, Dec 16, 2013
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    • "However, the mechanisms of scaffold assembly and its role in generating cellular responses remain unclear. A yeast scaffold protein, Ste5, involved in the mating MAP kinase pathway is known to function as a modular organizing center for the assembly of mating signaling proteins [7], [8]. Previous studies have revealed that individual docking interactions of Ste5 scaffold with its member kinases in the upper tier of the pathway -Ste11 (MAPKKK) and Ste7 (MAPKK)- could be functionally replaced by heterologous protein interactions and that such wiring was sufficient to restore pathway connectivity [9]. "
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    ABSTRACT: Formation of signaling protein complexes is crucial for proper signal transduction. Scaffold proteins in MAP kinase pathways are thought to facilitate complex assembly, thereby promoting efficient and specific signaling. To elucidate the assembly mechanism of scaffold complexes in mammals, we attempted to rationally rewire JIP1-dependent JNK MAP kinase pathway via alternative assembly of JIP1 complex. When JIP1-JNK docking interaction in the complex was replaced with heterologous protein interaction domains, such as PDZ domains and JNK-binding domains, a functional scaffold complex was reconstituted, and JNK signaling was rescued. Reassembly of JIP1 complex using heterologous protein interactions was sufficient for restoring of JNK MAP kinase pathway to induce signaling responses, including JNK activation and cell death. These results suggest a simple yet modular mechanism for JIP1 scaffold assembly in mammals.
    PLoS ONE 05/2014; 9(5):e96797. DOI:10.1371/journal.pone.0096797 · 3.23 Impact Factor
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    • "In the cytosol, signals can transmit through the large assemblies, such as the nucleosomes in the nucleus; and as we argue here, also through the structured cytoskeleton, which is similarly dynamic. In all cases, scaffolding proteins [103] [105] [106] which are sometimes overlooked in cellular diagrams are likely to play major roles. Scaffolding proteins do not communicate the signal passively; they can control it [103]. "
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    ABSTRACT: The spatial structure of the cell is highly organized at all levels: from small complexes and assemblies, to local nano- and microclusters, to global, micrometer scales across and between cells. We suggest that this multiscale spatial cell organization also organizes signaling and coordinates cellular behavior. We propose a new view of the spatial structure of cell signaling systems. This new view describes cell signaling in terms of dynamic allosteric interactions within and among distinct, spatially organized transient clusters. The clusters vary over time and space and are on length scales from nanometers to micrometers. When considered across these length scales, primary factors in the spatial organization are cell membrane domains and the actin cytoskeleton, both also highly dynamic. A key challenge is to understand the interplay across these multiple scales, link it to the physicochemical basis of the conformational behavior of single molecules and ultimately relate it to cellular function. Overall, our premise is that at these scales, cell signaling should be thought of not primarily as a sequence of diffusion-controlled molecular collisions, but instead transient, allostery-driven cluster re-forming interactions.
    Physical Biology 08/2013; 10(4):045004. DOI:10.1088/1478-3975/10/4/045004 · 2.54 Impact Factor
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    • "At the cortex, Ste5 simultaneously binds all the components of the MAPK module through distinct domains [18] and acts as a cofactor by increasing the low MAPKK Ste7 intrinsic phosphorylation activity on MAPK Fus3 [19]. Membrane binding also relieves an auto-inhibitory interaction in Ste5 to promote Fus3 activation [20]. Finally, Ste5, by binding to the phosphatase Ptc1, also promotes a switch-like activation of Fus3 [21]. "
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    ABSTRACT: Many cells are able to orient themselves in a non-uniform environment by responding to localized cues. This leads to a polarized cellular response, where the cell can either grow or move towards the cue source. Fungal haploid cells secrete pheromones to signal mating, and respond by growing a mating projection towards a potential mate. Upon contact of the two partner cells, these fuse to form a diploid zygote. In this review, we present our current knowledge on the processes of mating signalling, pheromone-dependent polarized growth and cell fusion in Saccharomyces cerevisiae and Schizosaccharomyces pombe, two highly divergent ascomycete yeast models. While the global architecture of the mating response is very similar between these two species, they differ significantly both in their mating physiologies and in the molecular connections between pheromone perception and downstream responses. The use of both yeast models helps enlighten both conserved solutions and species-specific adaptations to a general biological problem.
    Open Biology 03/2013; 3(3):130008. DOI:10.1098/rsob.130008 · 5.78 Impact Factor
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