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Dissertation/Thesis Abstract

Transient structure, flexibility, and function relationships in intrinsically unstructured protein regulators of protein phosphatase 1
by Dancheck, Barbara, Ph.D., Brown University, 2010, 309; 3430176
Abstract (Summary)

The discovery of intrinsically unstructured proteins (IUPs) challenged the idea that proteins require a stable 3-dimensional structure for their biological activity. IUPs are ensembles of rapidly exchanging conformers, and are functional in their unstructured state. However, they are not random coil polypeptide chains; rather, they often exhibit transient preferences for non-random structure. It is thought that this pre-organization and spatial restriction in IUPs enables a more efficient and specific binding to target molecules than a primary sequence alone. Therefore, transient structure in IUPs is essential for their function. Conserved structure function motifs in folded proteins allow for the prediction of protein function based on structure; thus, structure is intimately linked to function. However, the paucity of data regarding structural propensities in related IUPs has prevented a similar correlation between transient structure and IUP function. This thesis addresses the correlation of transient structure, flexibility and function within a group of related IUPs.

Biomolecular NMR spectroscopy and ensemble structure calculations were used to determine the secondary and tertiary structural propensities of three IUPs which all bind and regulate the essential ser/thr Protein Phosphatase 1 (PP1): the PP1 inhibitor proteins inhibitor-2 (I-2) and dopamine- and cAMP-regulated phosphoprotein with Mr 32,000 Da (DARPP-32), and the PP1 binding domain of the PP1 targeting protein spinophilin. Each of these regulatory proteins exhibits unique secondary and tertiary structural propensities in their unbound form that are correlated with their function. However, no conserved transient structure function motifs were identified in this group of PP1 regulators. This is likely due to the diverse ways in which these three proteins interact with PP1. The role of flexibility in IUP function was examined by monitoring changes which occur to the IUP regulators during the formation of the heterotrimeric PP1:spinophilin:I-2 complex (PSI). Upon binding to PP1, I-2 remains highly flexible while spinophilin becomes restricted to a single conformation. However, structural rearrangements can be detected in both proteins upon formation of PSI. This indicates that residual flexibility in IUPs after binding a target molecule allows for complex regulatory mechanisms not easily possible for folded protein regulators.

Indexing (document details)
Advisor: Peti, Wolfgang
School: Brown University
School Location: United States -- Rhode Island
Source: DAI-B 71/11, Dissertation Abstracts International
Subjects: Biophysics
Keywords: Protein phosphatase, Spinophilin, Unstructured protein
Publication Number: 3430176
ISBN: 978-1-124-30281-2
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