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Papers In Press, published online ahead of print July 6, 2004
Cardiovascular Research Center, University of Virginia, Charlottesville, VA 22908
Corresponding Author: nm3h{at}virginia.edu
Rho familRho family small GTPases are critical regulators of multiple cellular processes and activities. Dbl homology (DH)-containing proteins are the classical guanine nucleotide exchange factors (GEFs) responsible for activation of Rho proteins. Recently another group of mammalian Rho-GEFs was discovered that includes CDM (Ced-5, DOCK180, Myoblast city) proteins that activate Rac and zizimin1 that activates Cdc42 via a non-conventional GEF module that we named the CZH2 domain. We report here that zizimin1 dimerizes via the CZH2 domain and that dimers are the only form detected. Dimerization was mapped to a ~200 amino acid region that overlaps but is distinct from the Cdc42 binding sequences. Rotary shadowing electron microscopy revealed zizimin1 to be a symmetric, V-shaped, molecule. Experiments with DOCK180 and homology analysis suggest that dimerization may be a general feature of CZH proteins. Deletion and mutation analysis indicated existence of individual Cdc42 binding sites in the zizimin1 monomers. Kinetic measurements demonstrated increased binding affinity of Cdc42 to zizimin1 at higher Cdc42 concentration suggesting positive cooperativity. These features are likely to be critical for Cdc42 activation and GEF activity.
J. Biol. Chem, 10.1074/jbc.M404535200
Submitted on April 23, 2004
Revised on July 1, 2004
Accepted on July 6, 2004
The novel Cdc42 guanine nucleotide exchange factor, zizimin1, dimerizes via the Cdc42-binding CZH2 domain
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