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dc.contributor.author Smith, Nicholas Robert, 1981-
dc.date.accessioned 2011-06-20T19:05:39Z
dc.date.available 2011-06-20T19:05:39Z
dc.date.issued 2010-09
dc.identifier.uri http://hdl.handle.net/1794/11303
dc.description xiv, 81 p. : ill. (some col.) A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. en_US
dc.description.abstract Protein-protein interaction networks translate environmental inputs into specific physiological outputs. The signaling proteins in these networks require regulatory mechanisms to ensure proper molecular function. Two common regulatory features of signaling proteins are autoinhibition and ultrasensitivity. Autoinhibition locks the protein in an inactive state through cis interactions with a regulatory module until it is activated by a specific input signal. Ultrasensitivity, defined as steep activation after a threshold, allows cells to convert graded inputs into more switch-like outputs and can lead to complex decision making behaviors such as bistability. Although these mechanisms are common features of signaling proteins, their molecular origins are poorly understood. I used the Drosophila Pins protein, a regulator of spindle positioning in neuroblast cells, as a model to study the molecular origin and function of autoinhibition and ultrasensitivity. Pins and its binding partners. Gαi and Mud, form a signaling pathway required for coordinating spindle positioning with cellular polarity in Drosophila neuroblasts. I found Pins switches from an autoinhibited to an activate state by modular allostery. Gαi binding to the third of three GoLoco (GL) domains allows Pins to interact with the microtubule binding protein Mud. The GL3 region is required for autoinhibitoon, as amino acids upstream and within GL3 constitute this regulatory behavior. This autoinhibitory module is conserved in LGN, the mammalian Pins orthologue. I also demonstrated that Gαi activation of Pins is ultrasensitive. A Pins protein containing inactivating point mutations to GLs l and 2 exhibits non-ultrasensitive (graded) activation. Ultrasensitivity is required for Pins function in vivo as the graded Pins mutant fails to robustly orient the mitotic spindle. I considered two models for the source of ultrasensitivity in this pathway: cooperative or "decoy" Gai binding. I found ultrasensitivity arises from a decoy mechanism in which GLs 1 and 2 compete with the activating GL3 for the input, Gai. These findings suggest that molecular ultrasensitivity can be generated without cooperativity. This decoy mechanism is relatively simple, suggesting ultrasensitive responses can be evolved by the inclusion of domain repeats, a common feature observed in signaling proteins. This dissertation includes previously published and unpublished co-authored material. en_US
dc.description.sponsorship Committee in charge: Tom Stevens, Chairperson, Chemistry; Kenneth Prehoda, Member, Chemistry; Christopher Doe, Member, Biology; Peter von Hippel, Member, Chemistry; Karen Guillemin, Outside Member, Biology en_US
dc.language.iso en_US en_US
dc.publisher University of Oregon en_US
dc.relation.ispartofseries University of Oregon theses, Dept. of Chemistry, Ph. D., 2010;
dc.subject Autoinhibition en_US
dc.subject Ultrasensitivity en_US
dc.subject Spindle orientation en_US
dc.subject Asymmetric cell division en_US
dc.subject Neuroblast en_US
dc.subject Neurobiology en_US
dc.subject Biochemistry en_US
dc.title Autoinhibition and ultrasensitivity in the Galphai-Pins-Mud spindle orientation pathway en_US
dc.type Thesis en_US


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