title: A phosphodegron controls nutrient-induced proteasomal activation of the signaling protease Ssy5.
abstract: Regulated proteolysis serves as a mechanism to control cellular processes. The SPS (Ssy1-Ptr3-Ssy5) sensor in yeast responds to extracellular amino acids by endoproteolytically activating transcription factors Stp1 and Stp2 (Stp1/2). The processing endoprotease Ssy5 is regulated via proteasomal degradation of its noncovalently associated N-terminal prodomain. We find that degradation of the prodomain requires a conserved phosphodegron comprising phosphoacceptor sites and ubiquitin-accepting lysine residues. Upon amino acid induction, the phosphodegron is modified in a series of linked events by a set of general regulatory factors involved in diverse signaling pathways. First, an amino acid-induced conformational change triggers phosphodegron phosphorylation by the constitutively active plasma membrane-localized casein kinase I (Yck1/2). Next the prodomain becomes a substrate for polyubiquitylation by the Skp1/Cullin/Grr1 E3 ubiquitin ligase complex (SCF(Grr1)). Finally, the modified prodomain is concomitantly degraded by the 26S proteasome. These integrated events are requisite for unfettering the Ssy5 endoprotease, and thus Stp1/2 processing. The Ssy5 phosphoacceptor motif resembles the Yck1/2- and Grr1-dependent degrons of regulators in the Snf3/Rgt2 glucose-sensing pathway. Our work defines a novel proteolytic activation cascade that regulates an intracellular signaling protease and illustrates how general signaling components are recruited to distinct pathways that achieve conditional and specific signaling outputs.
authors.affiliation: Wenner-Gren Institute, Stockholm University, S-106 91 Stockholm, Sweden.
authors.forename: Deike J
authors.initials: DJ
authors.lastname: Omnus
authors.forename: Thorsten
authors.initials: T
authors.lastname: Pfirrmann
authors.forename: Claes
authors.initials: C
authors.lastname: Andréasson
authors.forename: Per O
authors.initials: PO
authors.lastname: Ljungdahl
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000378:metabolism / Q000494:pharmacology*; D015153:Blotting, Western; D047389:Casein Kinase I / Q000235:genetics / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects*; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary / Q000235:genetics; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D044843:SKP Cullin F-Box Protein Ligases / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D057057:Serine Proteases / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism; D054875:Ubiquitination / Q000187:drug effects
chemical_list: D000596:Amino Acids; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D016601:RNA-Binding Proteins; C074632:STP1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C421606:Stp2 protein, S cerevisiae; D014157:Transcription Factors; D044843:SKP Cullin F-Box Protein Ligases; D044767:Ubiquitin-Protein Ligases; D047389:Casein Kinase I; C479664:YCK1 protein, S cerevisiae; C479666:YCK2 protein, S cerevisiae; D057057:Serine Proteases; C550846:Ssy5 protein, S cerevisiae; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease