Research Article

The Ste5 Scaffold Allosterically Modulates Signaling Output of the Yeast Mating Pathway

Science  10 Feb 2006:
Vol. 311, Issue 5762, pp. 822-826
DOI: 10.1126/science.1120941

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Abstract

Scaffold proteins organize signaling proteins into pathways and are often viewed as passive assembly platforms. We found that the Ste5 scaffold has a more active role in the yeast mating pathway: A fragment of Ste5 allosterically activated autophosphorylation of the mitogen-activated protein kinase Fus3. The resulting form of Fus3 is partially active—it is phosphorylated on only one of two key residues in the activation loop. Unexpectedly, at a systems level, autoactivated Fus3 appears to have a negative regulatory role, promoting Ste5 phosphorylation and a decrease in pathway transcriptional output. Thus, scaffolds not only direct basic pathway connectivity but can precisely tune quantitative pathway input-output properties.

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