Proteomic Analysis of Unbounded Cellular Compartments: Synaptic Clefts.

Cellular compartments that cannot be biochemically isolated are challenging to characterize. Here we demonstrate the proteomic characterization of the synaptic clefts that exist at both excitatory and inhibitory synapses. Normal brain function relies on the careful balance of these opposing neural connections, and understanding how this balance is achieved relies on knowledge of their protein compositions. Using a spatially restricted enzymatic tagging strategy, we mapped the proteomes of two of the most common excitatory and inhibitory synaptic clefts in living neurons. These proteomes reveal dozens of synaptic candidates and assign numerous known synaptic proteins to a specific cleft type. The molecular differentiation of each cleft allowed us to identify Mdga2 as a potential specificity factor influencing Neuroligin-2's recruitment of presynaptic neurotransmitters at inhibitory synapses.

A Mechanical Switch Couples T Cell Receptor Triggering to the Cytoplasmic Juxtamembrane Regions of CD3ζζ.

The eight-subunit T cell receptor (TCR)-CD3 complex is the primary determinant for T cell fate decisions. Yet how it relays ligand-specific information across the cell membrane for conversion to chemical signals remains unresolved. We hypothesized that TCR engagement triggers a change in the spatial relationship between the associated CD3ζζ subunits at the junction where they emerge from the membrane into the cytoplasm. Using three in situ proximity assays based on ID-PRIME, FRET, and EPOR activity, we determined that the cytosolic juxtamembrane regions of the CD3ζζ subunits are spread apart upon assembly into the TCR-CD3 complex. TCR engagement then triggered their apposition. This mechanical switch resides upstream of the CD3ζζ intracellular motifs that initiate chemical signaling, as well as the polybasic stretches that regulate signal potentiation. These findings provide a framework from which to examine triggering events for activating immune receptors and other complex molecular machines.

Pharmacology of ionotropic glutamate receptors: A structural perspective.

The impact of structural biology on the design of ligands (agonists, antagonists and modulators) for ionotropic glutamate receptors is reviewed.

Directed Synthesis of All Four Pure Stereoisomers of the N,C-Coupled Naphthylisoquinoline Alkaloid Ancistrocladinium A.

The first preparation of the N,C-coupled naphthylisoquinoline alkaloid ancistrocladinium A and its likewise naturally occurring minor atropisomer, in an atropisomerically pure form, is described. The synthesis succeeded by resolution of the already rotationally hindered, and thus atropo-diastereomeric acetamide precursors, which were then, without major loss of stereochemical information, cyclized to the respective target molecules. The strategy was applied to the first synthesis of the regioisomeric product ancistrocladinium D, likewise in a stereochemically pure form.

Photocontrol of AMPA receptors with a photochromic ligand.

Photochromic ligands (PCLs), recently introduced by our group as a tool for researchers in neuroscience, offer the ability to control native receptors with light in a reversible fashion without the need for any genetic manipulation. Here we describe the application of the PCL Azo-Tetrazole-AMPA-3 (ATA-3) to reversibly gate native AMPA-receptors with blue light and thereby control the activity of cortical neurons in brain slices.

Optical control of metabotropic glutamate receptors.

G protein-coupled receptors (GPCRs), the largest family of membrane signaling proteins, respond to neurotransmitters, hormones and small environmental molecules. The neuronal function of many GPCRs has been difficult to resolve because of an inability to gate them with subtype specificity, spatial precision, speed and reversibility. To address this, we developed an approach for opto-chemical engineering of native GPCRs. We applied this to the metabotropic glutamate receptors (mGluRs) to generate light-agonized and light-antagonized mGluRs (LimGluRs). The light-agonized LimGluR2, on which we focused, was fast, bistable and supported multiple rounds of on/off switching. Light gated two of the primary neuronal functions of mGluR2: suppression of excitability and inhibition of neurotransmitter release. We found that the light-antagonized tool LimGluR2-block was able to manipulate negative feedback of synaptically released glutamate on transmitter release. We generalized the optical control to two additional family members: mGluR3 and mGluR6. This system worked in rodent brain slices and in zebrafish in vivo, where we found that mGluR2 modulated the threshold for escape behavior. These light-gated mGluRs pave the way for determining the roles of mGluRs in synaptic plasticity, memory and disease.