title: Recruitment of scribble to the synaptic scaffolding complex requires GUK-holder, a novel DLG binding protein.
abstract: BACKGROUND
  Membrane-associated guanylate kinases (MAGUKs), such as Discs-Large (DLG), play critical roles in synapse maturation by regulating the assembly of synaptic multiprotein complexes. Previous studies have revealed a genetic interaction between DLG and another PDZ scaffolding protein, SCRIBBLE (SCRIB), during the establishment of cell polarity in developing epithelia. A possible interaction between DLG and SCRIB at synaptic junctions has not yet been addressed. Likewise, the biochemical nature of this interaction remains elusive, raising questions regarding the mechanisms by which the actions of both proteins are coordinated.
  
  
  RESULTS
  Here we report the isolation of a new DLG-interacting protein, GUK-holder, that interacts with the GUK domain of DLG and which is dynamically expressed during synaptic bouton budding. We also show that at Drosophila synapses DLG colocalizes with SCRIB and that this colocalization is likely to be mediated by direct interactions between GUKH and the PDZ2 domain of SCRIB. We show that DLG, GUKH, and SCRIB form a tripartite complex at synapses, in which DLG and GUKH are required for the proper synaptic localization of SCRIB.
  
  
  CONCLUSIONS
  Our results provide a mechanism by which developmentally important PDZ-mediated complexes are associated at the synapse.
authors.affiliation: Department of Biology and Molecular and Cellular Biology Program, University of Massachusetts, Amherst, MA 01003, USA.
authors.forename: Dennis
authors.initials: D
authors.lastname: Mathew
authors.forename: L Sian
authors.initials: LS
authors.lastname: Gramates
authors.forename: Mary
authors.initials: M
authors.lastname: Packard
authors.forename: Ulrich
authors.initials: U
authors.lastname: Thomas
authors.forename: David
authors.initials: D
authors.lastname: Bilder
authors.forename: Norbert
authors.initials: N
authors.lastname: Perrimon
authors.forename: Michael
authors.initials: M
authors.lastname: Gorczyca
authors.forename: Vivian
authors.initials: V
authors.lastname: Budnik
mesh_terms: D000818:Animals; D029721:Drosophila Proteins; D004331:Drosophila melanogaster; D051528:Guanylate Kinases; D019476:Insect Proteins / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D009703:Nucleoside-Phosphate Kinase / Q000235:genetics / Q000378:metabolism*; D013569:Synapses / Q000378:metabolism*; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D029721:Drosophila Proteins; D019476:Insect Proteins; D008565:Membrane Proteins; C404683:Scrib protein, Drosophila; D025521:Tumor Suppressor Proteins; C070350:dlg1 protein, Drosophila; D009703:Nucleoside-Phosphate Kinase; D051528:Guanylate Kinases