title: The active zone protein CAST directly associates with Ligand-of-Numb protein X.
abstract: The presynaptic active zone (AZ) is a specialized site where neurotransmitter release occurs in a precisely regulated manner. The cytomatrix at the AZ (CAZ)-associated protein CAST and its family member ELKS form a large molecular complex at the AZ and regulate neurotransmitter release by binding other AZ proteins including Bassoon, Piccolo, Munc13-1, and RIM1. Here, yeast two-hybrid screening was used to identify Ligand-of-Numb Protein X (LNX) as a potential binding partner for CAST. LNX is an interactor of Numb and has four PDZ domains. CAST bound LNX both in vivo and in vitro. This binding required the COOH-terminus of CAST and the second PDZ domain of LNX. CAST and LNX were further colocalized with each other in a heterologous expression system, in which LNX was recruited to a Triton X-insoluble structure. Moreover, exogenously expressed LNX was partially colocalized with endogenous CAST in the axonal varicosities of cultured rat hippocampal neurons. These results suggest that CAST and LNX might form a protein complex in neurons.
authors.affiliation: Department of Clinical and Molecular Pathology, Graduate School of Medicine/Faculty of Medicine, University of Toyama, Toyama 930-0194, Japan.
authors.forename: Susumu
authors.initials: S
authors.lastname: Higa
authors.forename: Takashi
authors.initials: T
authors.lastname: Tokoro
authors.forename: Eiji
authors.initials: E
authors.lastname: Inoue
authors.forename: Isao
authors.initials: I
authors.lastname: Kitajima
authors.forename: Toshihisa
authors.initials: T
authors.lastname: Ohtsuka
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D006624:Hippocampus / Q000378:metabolism; D008024:Ligands; D008565:Membrane Proteins / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D018377:Neurotransmitter Agents / Q000378:metabolism*; D017729:Presynaptic Terminals / Q000378:metabolism*; D051381:Rats; D013501:Surface-Active Agents / Q000737:chemistry
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C479909:ERC1 protein, rat; D008024:Ligands; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D018377:Neurotransmitter Agents; D013501:Surface-Active Agents