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Title: Structural studies of the interactions between the nuclear protein export factor CRM1 and its partners
Author: Fox, A. M.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2010
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To investigate the position of the C-terminal helix in unbound CRM1/Xpo1p, SAXS was used to compare the solution conformations of CRM1/Xpo1p to the known crystal structures. This study indicated that the C-terminal helix is likely to lie across the toroid when neither RanGTP nor NES cargo is bound. Removing the C-terminal helix leads to an increase in the affinity of CRM1 for the NES in the absence of RanGTP, essentially uncoupling the co-operativity of the binding process. Binding studies of further CRM1 mutants suggested that a series of highly conserved acidic residues at the tip of the C-terminal helix (that are not seen in the crystal structures) bind to conserved basic residues located near the HEAT repeats of the NES binding site. The putative electrostatic interaction between the C-terminal helix and these basic residues appears to contribute to a process that stabilises the NES-binding HEAT repeats in a conformation that reduces the affinity for the NES. The collected findings from the SAXS studies of CRM1 and the mutagenesis experiments led to the development of a new model for the mechanism by which RanGTP regulates the binding of NES cargoes to CRM1. The model proposes that the HEAT 9 loop and the C-terminal helix of CRM1 together have an allosteric inhibitory effect at the NES binding region that is altered when RanGTP binds and that this mechanism, rather than the influence of global changes in the shape of the CRM1 toroid, is the central basis of the co-operative binding of NES cargoes and RanGTP to CRM1.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available