title: Substrate competition as a source of ultrasensitivity in the inactivation of Wee1.
abstract: The mitotic regulators Wee1 and Cdk1 can inactivate each other through inhibitory phosphorylations. This double-negative feedback loop is part of a bistable trigger that makes the transition into mitosis abrupt and decisive. To generate a bistable response, some component of a double-negative feedback loop must exhibit an ultrasensitive response to its upstream regulator. Here, we experimentally demonstrate that Wee1 exhibits a highly ultrasensitive response to Cdk1. Several mechanisms can, in principle, give rise to ultrasensitivity, including zero-order effects, multisite phosphorylation, and competition mechanisms. We found that the ultrasensitivity in the inactivation of Wee1 arises mainly through two competition mechanisms: competition between two sets of phosphorylation sites in Wee1 and between Wee1 and other high-affinity Cdk1 targets. Based on these findings, we were able to reconstitute a highly ultrasensitive Wee1 response with purified components. Competition provides a simple way of generating the equivalent of a highly cooperative allosteric response.
authors: Department of Chemical and Systems Biology, Stanford University School of Medicine, Center for Clinical Sciences Research, Stanford, CA 94305-5174, USA.
authors: Sun Young
authors: SY
authors: Kim
authors: James E
authors: JE
authors: Ferrell
mesh_terms: D000818:Animals; D016203:CDC2 Protein Kinase / Q000235:genetics / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019926:Cyclin B / Q000378:metabolism; D025461:Feedback, Physiological; D007700:Kinetics; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009865:Oocytes / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012617:Sea Urchins; D013912:Threonine / Q000378:metabolism; D029867:Xenopus Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: D018797:Cell Cycle Proteins; D019926:Cyclin B; D009687:Nuclear Proteins; D011994:Recombinant Proteins; D029867:Xenopus Proteins; D013912:Threonine; C530005:WEE1 protein, Xenopus; D011505:Protein-Tyrosine Kinases; D016203:CDC2 Protein Kinase