The Structural Basis for Cdc42-Induced Dimerization of IQGAPs

Louis LeCour Jr; Vamsi K Boyapati; Jing Liu; Zhigang Li; David B Sacks; David K Worthylake

doi:10.1016/j.str.2016.06.016

The Structural Basis for Cdc42-Induced Dimerization of IQGAPs

Structure. 2016 Sep 6;24(9):1499-508. doi: 10.1016/j.str.2016.06.016. Epub 2016 Aug 11.

Authors

Louis LeCour Jr¹, Vamsi K Boyapati¹, Jing Liu¹, Zhigang Li², David B Sacks², David K Worthylake³

Affiliations

¹ Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, New Orleans, LA 70112, USA.
² Department of Laboratory Medicine, National Institutes of Health Clinical Center, Bethesda, MD 20892, USA.
³ Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, New Orleans, LA 70112, USA. Electronic address: dworth@lsuhsc.edu.

Abstract

In signaling, Rho-family GTPases bind effector proteins and alter their behavior. Here we present the crystal structure of Cdc42·GTP bound to the GTPase-activating protein (GAP)-related domain (GRD) of IQGAP2. Four molecules of Cdc42 are bound to two GRD molecules, which bind each other in a parallel dimer. Two Cdc42s bind very similarly to the Ras/RasGAP interaction, while the other two bind primarily to "extra domain" sequences from both GRDs, tying the GRDs together. Calorimetry confirms two-site binding of Cdc42·GTP for the GRDs of both IQGAP2 and IQGAP1. Mutation of important extra domain residues reduces binding to single-site and abrogates Cdc42 binding to a much larger IQGAP1 fragment. Importantly, Rac1·GTP displays only single-site binding to the GRDs, indicating that only Cdc42 promotes IQGAP dimerization. The structure identifies an unexpected role for Cdc42 in protein dimerization, thus expanding the repertoire of interactions of Ras family proteins with their targets.

MeSH terms

Amino Acid Motifs
Binding Sites
Cloning, Molecular
Crystallography, X-Ray
Escherichia coli / genetics
Escherichia coli / metabolism
Gene Expression
Guanosine Triphosphate / chemistry*
Guanosine Triphosphate / metabolism
Humans
Models, Molecular
Mutation
Protein Binding
Protein Conformation, alpha-Helical
Protein Conformation, beta-Strand
Protein Interaction Domains and Motifs
Protein Multimerization
Recombinant Proteins / chemistry
Recombinant Proteins / genetics
Recombinant Proteins / metabolism
cdc42 GTP-Binding Protein / chemistry*
cdc42 GTP-Binding Protein / genetics
cdc42 GTP-Binding Protein / metabolism
rac1 GTP-Binding Protein / chemistry*
rac1 GTP-Binding Protein / genetics
rac1 GTP-Binding Protein / metabolism
ras GTPase-Activating Proteins / chemistry*
ras GTPase-Activating Proteins / genetics
ras GTPase-Activating Proteins / metabolism

Substances

IQ motif containing GTPase activating protein 1
IQGAP2 protein, human
RAC1 protein, human
Recombinant Proteins
ras GTPase-Activating Proteins
Guanosine Triphosphate
cdc42 GTP-Binding Protein
rac1 GTP-Binding Protein

Grants and funding

R01 GM084072/GM/NIGMS NIH HHS/United States