Trio, a Rho Family GEF, Interacts with the Presynaptic Active Zone Proteins Piccolo and Bassoon.

Dhananjay Wagh,Laurence Florens,Ryan T Terry-Lorenzo,Richard J Reimer,Michael P Washburn,Viviana I Torres,Clarissa L Waites,Selene K Swanson,Eckart D Gundelfinger,Jose Galaz,Craig C Garner

doi:10.1371/journal.pone.0167535

Abstract

Synaptic vesicles (SVs) fuse with the plasma membrane at a precise location called the presynaptic active zone (AZ). This fusion is coordinated by proteins embedded within a cytoskeletal matrix assembled at the AZ (CAZ). In the present study, we have identified a novel binding partner for the CAZ proteins Piccolo and Bassoon. This interacting protein, Trio, is a member of the Dbl family of guanine nucleotide exchange factors (GEFs) known to regulate the dynamic assembly of actin and growth factor dependent axon guidance and synaptic growth. Trio was found to interact with the C-terminal PBH 9/10 domains of Piccolo and Bassoon via its own N-terminal Spectrin repeats, a domain that is also critical for its localization to the CAZ. Moreover, our data suggest that regions within the C-terminus of Trio negatively regulate its interactions with Piccolo/Bassoon. These findings provide a mechanism for the presynaptic targeting of Trio and support a model in which Piccolo and Bassoon play a role in regulating neurotransmission through interactions with proteins, including Trio, that modulate the dynamic assembly of F-actin during cycles of synaptic vesicle exo- and endocytosis.

Highlights

Active zones (AZ) are specialized regions of the presynaptic plasma membrane of neurons designed to regulate the activity-dependent release of neurotransmitter [1]
The purification of active zone-specific protein complexes has been hampered by the inability to biochemically separate the cytoskeletal matrix assembled at the AZ (CAZ) from its corresponding postsynaptic compartment, the postsynaptic density (PSD) [51]
To identify in vivo protein complexes formed by Piccolo and Bassoon, we developed a biochemical strategy that took advantage of the fact that these proteins are transported to synapses on vesicles with other AZ proteins, such as ELKS but not with synaptic vesicle (SV) or postsynaptic proteins in the developing brain [35, 38, 52]

Summary

Introduction

Active zones (AZ) are specialized regions of the presynaptic plasma membrane of neurons designed to regulate the activity-dependent release of neurotransmitter [1]. AZ proteins are thought to function in concert with trans-synaptic cell-adhesion molecules (CAMs) to define sites of neurotransmitter release, holding them in register with the postsynaptic density (PSD) [1, 2]. They are thought to precisely coordinate aspects of the synaptic vesicle (SV) cycle [3] such as the translocation of SVs from the reserve to the readily releasable pool, and SV exocytosis/endocytosis [1]. In photoreceptor cell ribbon synapses lacking Bassoon, the ribbons, specialized structures of the CAZ, are detached from the presynaptic membrane, impairing vision [9]

Methods

Results

Conclusion