Bond swapping from a charge cloud allows flexible coordination of upstream signals through WASP: Multiple regulatory roles for the WASP basic region.

Tetley, George JN 
Szeto, Aydan 
Fountain, Adam J 
Mott, Helen R 

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Wiskott-Aldrich syndrome protein (WASP) activates the actin-related protein 2/3 homolog (Arp2/3) complex and regulates actin polymerization in a physiological setting. Cell division cycle 42 (Cdc42) is a key activator of WASP, which binds Cdc42 through a Cdc42/Rac-interactive binding (CRIB)-containing region that defines a subset of Cdc42 effectors. Here, using site-directed mutagenesis and binding affinity determination and kinetic assays, we report the results of an investigation into the energetic contributions of individual WASP residues to both the Cdc42-WASP binding interface and the kinetics of complex formation. Our results support the previously proposed dock-and-coalesce binding mechanism, initiated by electrostatic steering driven by WASP's basic region and followed by a coalescence phase likely driven by the conserved CRIB motif. The WASP basic region, however, appears also to play a role in the final complex, as its mutation affected both on- and off-rates, suggesting a more comprehensive physiological role for this region centered on the C-terminal triad of positive residues. These results highlight the expanding roles of the basic region in WASP and other CRIB-containing effector proteins in regulating complex cellular processes and coordinating multiple input signals. The data presented improve our understanding of the Cdc42-WASP interface and also add to the body of information available for Cdc42-effector complex formation, therapeutic targeting of which has promise for Ras-driven cancers. Our findings suggest that combining high-affinity peptide-binding sequences with short electrostatic steering sequences could increase the efficacy of peptidomimetic candidates designed to interfere with Cdc42 signaling in cancer.

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CDC42, cell signaling, cytoskeleton, intrinsically disordered protein, protein conformation, protein motif, protein–protein interaction, small GTPase, structure–function, thermodynamics, Actins, Amino Acid Sequence, Animals, Binding Sites, Crystallography, X-Ray, Humans, Kinetics, Neoplasms, Protein Binding, Regulatory Sequences, Nucleic Acid, Signal Transduction, Wiskott-Aldrich Syndrome, Wiskott-Aldrich Syndrome Protein, cdc42 GTP-Binding Protein, ras Proteins
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J Biol Chem
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Elsevier BV
MRC (MR/K017101/1)