PDBsum entry 2fa2

Transferase

PDB id: 2fa2

Contents

Protein chains

333 a.a.

Ligands

SCN ×6

Waters ×27

References listed in PDB file

Key reference

Title

The ste5 scaffold allosterically modulates signaling output of the yeast mating pathway.

Authors

R.P.Bhattacharyya, A.Reményi, M.C.Good, C.J.Bashor, A.M.Falick, W.A.Lim.

Ref.

Science, 2006, 311, 822-826. [DOI no: 10.1126/science.1120941]

PubMed id

16424299

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.

Figure 1.
Fig. 1. Fus3 recruitment to the pheromone response MAPK complex. (A) Schematic of pheromone response MAPK complex. The MAPK Fus3 interacts with the scaffold protein Ste5 (4–6) and the MAPKK Ste7 (6, 40). (B) Maps of the interaction domains in the MAPKK Ste7 and the scaffold Ste5. Minimal Fus3 binding peptides are shown in color [dark blue, Ste7_pep1 (12, 16); light blue, Ste7_pep2 (16)]. Black bars above the Ste5 schematic indicate protein-interaction domains identified in yeast two-hybrid assays (4, 37). The Fus3 binding peptide (Ste5_pep) is shown in red (fig. S1).

Figure 2.
Fig. 2. Structure of Fus3-Ste5 complex and comparison to canonical docking complexes. (A) Crystal structure of Fus3/Ste5_pep complex. Ste5 (red) binds to Fus3 in a bipartite manner. Close-up views of site A and site B on the right are shown with simulated annealed electron density omit maps (contoured at 1 ) for the Ste5 peptide. (B) Structure of Fus3 in complex with a canonical docking motif from Ste7 (Ste7_pep1) (16). (C) Protein-protein interactions at site A. The N-terminal half of Ste5_pep adopts a ß-strand conformation and initiates the formation of a new ß strand at the N terminus of Fus3 (ß0). This strand forms eight backbone-backbone H bonds with the Fus3 N-terminal region (H bonds are indicated with red dashed lines). The side chain of Q^292 is H bonded to the backbone of ß1, the hydrophobic side chain of I^294 interacts with a groove on the top of the kinase, and Y^295 makes an H bond with the side chain of R^4 from Fus3. Schematic illustration of secondary structural elements of the N-terminal kinase lobe in the unliganded and Ste5_pep liganded complex is shown on the right. (D) Comparison of protein-protein interactions at the canonical MAPK docking groove (site B) between the Fus3/Ste5_pep and the Fus3/Far1_pep complexes (16).

The above figures are reprinted by permission from the AAAs: Science (2006, 311, 822-826) copyright 2006.