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Structural and biochemical characterisation of PKCι assemblies and substrate targeting mechanisms

Ivanova, M; (2017) Structural and biochemical characterisation of PKCι assemblies and substrate targeting mechanisms. Doctoral thesis , UCL (University College London).

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Abstract

The PKCι (protein kinase C isoform ι) plays crucial roles in the formation and maintenance of cell polarity through the formation of the Par complex (PKCι, Par6, Cdc42, Par3), a master regulator of epithelial apical-basal polarity. The Par complex is an apical polarity marker and is directly opposed by the baso-lateral markers Lgl, Dlg and Scribble by mutual antagonism. The molecular basis for the mutual antagonism between the complexes is unclear but may involve direct inhibition of PKCι activity. Conversely, several proteins able to inhibit PKCι are also functionally validated substrates, for example Lgl, Par3 and Kibra. The focus of this thesis has been to explore the molecular details of PKCι regulation and RIPR-dependent substrate recruitment. Different forms of PKCι have been characterised using biophysical, biochemical and structural biology methods. An active mature PKCι kinase domain structure was defined at high resolution. Comparison with a Par3-inhibited conformer reveals how inhibition perturbs the active conformer. To probe the molecular interaction between PKCι and RIPR-dependent substrates, Llgl1 and Periphillin1, peptides from these proteins were characterised and crystallised with the PKCι kinase domain. Amino-terminal sequences flanking their PKC consensus motif make contacts exclusively with the PKCι C-lobe. Surprisingly, both Llgl1 and Periphillin1 peptides structures lacked a bound nucleotide within of PKCι. In contrast, an ATP-bound PKCι lacked the Periphillin substrate peptide. These data suggest that RIPR-dependent substrate peptides may influence nucleotide loading of PKCι. Finally, the thesis explored a second mechanism for Par6-PKCι recruitment to the apical domain through Crb-Pals1 interaction. The basis for Crb intracellular domain interaction with Pals1 and the Par complex was defined indicating contacts from the Pals-PDZ-SH3 unit are required to engage Crb. The higher Pals1 affinity for Crb than the Par complex, suggests a hierarchy of substrate interactions to recruit Par6-PKCι through the Crb complex.

Type: Thesis (Doctoral)
Title: Structural and biochemical characterisation of PKCι assemblies and substrate targeting mechanisms
Event: University College London
Language: English
UCL classification: UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences
URI: http://discovery.ucl.ac.uk/id/eprint/1537315
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