A docking site determining specificity of Pbs2 MAPKK for Ssk2/Ssk22 MAPKKKs in the yeast HOG pathway

• Published in: The EMBO journal 2003-07, Vol.22 (14), p.3624-3634
• Main Authors: Tatebayashi, Kazuo, Takekawa, Mutsuhiro, Saito, Haruo
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Cell Nucleus - metabolism; docking site; EMBO37; Enzyme Activation; Fungal Proteins - genetics; Fungal Proteins - metabolism; HOG pathway; Intracellular Signaling Peptides and Proteins; MAP kinase cascade; MAP Kinase Kinase Kinases - genetics; MAP Kinase Kinase Kinases - metabolism; MAP Kinase Signaling System; Membrane Proteins - metabolism; Mitogen-Activated Protein Kinase Kinases - chemistry; Mitogen-Activated Protein Kinase Kinases - genetics; Mitogen-Activated Protein Kinase Kinases - metabolism; Mitogen-Activated Protein Kinases - metabolism; Models, Biological; Molecular Sequence Data; Mutation; Osmotic Pressure; Pbs2; Protein Binding; Protein Kinases - metabolism; Protein Structure, Tertiary; Protein-Serine-Threonine Kinases - chemistry; Protein-Serine-Threonine Kinases - metabolism; Recombinant Fusion Proteins - metabolism; Saccharomyces cerevisiae - enzymology; Saccharomyces cerevisiae - metabolism; Saccharomyces cerevisiae Proteins - chemistry; Saccharomyces cerevisiae Proteins - metabolism; Signal Transduction; Yeasts
• ISSN: 0261-4189; 1460-2075; 1460-2075
• DOI: 10.1093/emboj/cdg353

Mitogen‐activated protein kinase (MAPK) cascades are conserved signaling modules composed of three sequentially activated kinases (MAPKKK, MAPKK and MAPK). Because individual cells contain multiple MAPK cascades, mechanisms are required to ensure the fidelity of signal transmission. In yeast, external high osmolarity activates the HOG (high osmolarity glycerol) MAPK pathway, which consists of two upstream branches (SHO1 and SLN1) and common downstream elements including the Pbs2 MAPKK and the Hog1 MAPK. The Ssk2/Ssk22 MAPKKKs in the SLN1 branch, when activated, exclusively phosphorylate the Pbs2 MAPKK. We found that this was due to an Ssk2/Ssk22‐specific docking site in the Pbs2 N‐terminal region. The Pbs2 docking site constitutively bound the Ssk2/Ssk22 kinase domain. Docking site mutations drastically reduced the Pbs2–Ssk2/Ssk22 interaction and hampered Hog1 activation by the SLN1 branch. Fusion of the Pbs2 docking site to a different MAPKK, Ste7, allowed phosphorylation of Ste7 by Ssk2/Ssk22. Thus, the docking site contributes to both the efficiency and specificity of signaling. During these analyses, we also found a nuclear export signal and a possible nuclear localization signal in Pbs2.