title: Secondary PDZ domain-binding site on class B plexins enhances the affinity for PDZ-RhoGEF.
abstract: PDZ domains are abundant protein interaction modules and typically recognize a short motif at the C terminus of their ligands, with a few residues in the motif endowing the binding specificity. The sequence-based rules, however, cannot fully account for the specificity between the vast number of PDZ domains and ligands in the cell. Plexins are transmembrane receptors that regulate processes such as axon guidance and angiogenesis. Two related guanine nucleotide exchange factors (GEFs), PDZ-RhoGEF and leukemia-associated RhoGEF (LARG), use their PDZ domains to bind class B plexins and play critical roles in signaling. Here, we present the crystal structure of the full-length cytoplasmic region of PlexinB2 in complex with the PDZ domain of PDZ-RhoGEF. The structure reveals that, in addition to the canonical C-terminal motif/PDZ interaction, the 3D domain of PlexinB2 forms a secondary interface with the PDZ domain. Our biophysical and cell-based assays show that the secondary interface contributes to the specific interaction between plexin and PDZ-RhoGEF and to signaling by plexin in the cell. Formation of secondary interfaces may be a general mechanism for increasing affinity and specificity of modular domain-mediated interactions.
authors.affiliation: Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX 75390;
authors.forename: Heath G
authors.initials: HG
authors.lastname: Pascoe
authors.affiliation: Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX 75390;
authors.forename: Stephen
authors.initials: S
authors.lastname: Gutowski
authors.affiliation: Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX 75390;
authors.forename: Hua
authors.initials: H
authors.lastname: Chen
authors.affiliation: Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX 75390.
authors.forename: Chad A
authors.initials: CA
authors.lastname: Brautigam
authors.affiliation: Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX 75390.
authors.forename: Zhe
authors.initials: Z
authors.lastname: Chen
authors.affiliation: Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX 75390;
authors.forename: Paul C
authors.initials: PC
authors.lastname: Sternweis
authors.affiliation: Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX 75390; Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX 75390 xuewu.zhang@utsouthwestern.edu.
authors.forename: Xuewu
authors.initials: X
authors.lastname: Zhang
mesh_terms: D020816:Amino Acid Motifs; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D054731:PDZ Domains; D011485:Protein Binding / Q000235:genetics; D017434:Protein Structure, Tertiary; D064067:Rho Guanine Nucleotide Exchange Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: C577222:ARHGEF12 protein, human; D009419:Nerve Tissue Proteins; C000604175:PLXNB2 protein, human; D064067:Rho Guanine Nucleotide Exchange Factors
keywords: PDZ; plexin; protein interaction module; signaling; specificity