ATP and MO25α Regulate the Conformational State of the STRADα Pseudokinase and Activation of the LKB1 Tumour Suppressor

Elton Zeqiraj,Iva Navratilova,Maria Deak,Jérôme Boudeau,Beatrice Maria Filippi,Dario R Alessi,Daan M F Van Aalten,Simon Goldie,Daniel Herschlag

doi:10.1371/journal.pbio.1000126

Elton Zeqiraj, Iva Navratilova + Show 7 more

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https://doi.org/10.1371/journal.pbio.1000126

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Abstract

Author SummaryThere are 518 human protein kinases that are responsible for orchestrating the phosphorylation-dependant signal transduction events that regulate almost all cellular processes. Curiously, approximately 10% of protein kinases lack one or more catalytic residues, and these kinases have been termed pseudokinases. It has been proposed that some pseudokinases act as scaffolds, bringing together proteins involved in signalling networks. Here, we report the structure of the pseudokinase STRADα in complex with the adaptor protein MO25α; together these two proteins regulate the LKB1 tumour suppressor kinase. Despite lacking several key catalytic residues, STRADα binds ATP and adopts an active conformation typical of catalytically competent kinases. The affinity of STRADα for ATP is enhanced by MO25α and vice versa. We go on to demonstrate through mutagenesis studies that binding to both ATP and MO25α is essential for the activation of LKB1. Our data suggest that STRADα exerts its functions through an active conformation, not through actual catalytic activity, thus raising the possibility that pseudokinases regulate signalling networks by adopting different structural conformations.

Highlights

Pseudokinases are classified as protein kinases that lack key catalytic residues within their kinase domain [1,2]
We focused on the interaction between the STRADa pseudokinase domain and full-length MO25a
These proteins were coexpressed in Escherichia coli and the STRADa/MO25a complex eluted as a heterodimer of the expected size from a gel filtration column, yielding approximately 60 mg of the complex from 4 l of culture (Figure S1)

Summary

Introduction

Pseudokinases are classified as protein kinases that lack key catalytic residues within their kinase domain [1,2]. These proteins are emerging as important regulators and scaffolding components of various signal transduction networks [2]. Despite being predicted to lack intrinsic kinase activity, several ‘‘pseudokinases’’ such as WNK, CASK, and IRAK2 still possess the ability to phosphorylate substrates. Recent data indicate that the IRAK2 pseudokinase, despite lacking the Mg2+ binding DFG motif as well as the catalytic HRD motif, still possesses activity [6]

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