title: Ssp2 Binding Activates the Smk1 Mitogen-Activated Protein Kinase.
abstract: Smk1 is a meiosis-specific mitogen-activated protein kinase (MAPK) inSaccharomyces cerevisiaethat couples spore morphogenesis to the completion of chromosome segregation. Similar to other MAPKs, Smk1 is controlled by phosphorylation of a threonine (T) and a tyrosine (Y) in its activation loop. However, it is not activated by a dual-specificity MAPK kinase. Instead, T207 in Smk1's activation loop is phosphorylated by the cyclin-dependent kinase (CDK)-activating kinase (Cak1), and Y209 is autophosphorylated in an intramolecular reaction that requires the meiosis-specific protein Ssp2. In this study, we show that Smk1 is catalytically inert unless it is bound by Ssp2. While Ssp2 binding activates Smk1 by a mechanism that is independent of activation loop phosphorylation, binding also triggers autophosphorylation of Y209 in Smk1, which, along with Cak1-mediated phosphorylation of T207, further activates the kinase. Autophosphorylation of Smk1 on Y209 also appears to modify the specificity of the MAPK by suppressing Y kinase and enhancing S/T kinase activity. We also found that the phosphoconsensus motif preference of Ssp2/Smk1 is more extensive than that of other characterized MAPKs. This study therefore defines a novel mechanism of MAPK activation requiring binding of an activator and also shows that MAPKs can be diversified to recognize unique phosphorylation motifs.
authors.affiliation: Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.
authors.forename: Chong Wai
authors.initials: CW
authors.lastname: Tio
authors.affiliation: Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.
authors.forename: Gregory
authors.initials: G
authors.lastname: Omerza
authors.affiliation: Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.
authors.forename: Timothy
authors.initials: T
authors.lastname: Phillips
authors.affiliation: Department of Pharmacology, Yale University, New Haven, Connecticut, USA.
authors.forename: Hua Jane
authors.initials: HJ
authors.lastname: Lou
authors.affiliation: Department of Pharmacology, Yale University, New Haven, Connecticut, USA.
authors.forename: Benjamin E
authors.initials: BE
authors.lastname: Turk
authors.affiliation: Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA edward.winter@jefferson.edu.
authors.forename: Edward
authors.initials: E
authors.lastname: Winter
mesh_terms: D004789:Enzyme Activation; D015966:Gene Expression Regulation, Fungal; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010766:Phosphorylation; D012441:Saccharomyces cerevisiae / Q000254:growth & development / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism*
chemical_list: C460039:SSP2 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D014443:Tyrosine; D020928:Mitogen-Activated Protein Kinases; C443670:Smk1 protein, S cerevisiae
keywords: MAPK; autophosphorylation; meiosis; mitogen-activated protein kinases; yeast