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    Chang Laboratory

    photo of researcher yongchang chang

    Yongchang Chang, MD, PhD

    Laboratory Focus

    Communication between neurons is the basic form of information processing in the brain. This communication occurs primarily in neuronal synapses, a small gap between an axon of one neuron and the dendrite of another. Chemicals called neurotransmitters are released by the axon. Neurotransmitter-operated ion channels (commonly called ligand-gated ion channels) open in response to a neurotransmitter binding at the receptor. Specific ions then flow through the open channels in the membrane. The charged ions flowing through the channels alter the membrane potential and control the excitability of the postsynaptic neurons.

    TChang Labhe major research interest in our laboratory is the structural basis of channel function in the cys-loop receptor family of ligand-gated ion channels. The cys-loop receptor family of ligand-gated ion channels has a pentameric structure. That is, five subunits form a functional channel (see figure, right). This receptor family includes nicotinic receptors, serotonin receptor type 3, GABAA/C receptors, glycine receptors, and zinc-activated cation channels. These receptors play important roles in mediating fast chemical synaptic transmission.

    Dysfunction of these receptor/channels is implicated in the origin of a variety neurological and psychiatric disorders, including epilepsy, anxiety, schizophrenia, smoking addiction, and neurodegenerative diseases. The cys-loop receptors are also the targets for many clinically useful neuroactive compounds such as benzodiazepines, barbiturates, neurosteroids, and general anesthetics. Therefore, gaining insight into the mechanisms of the cys-loop receptor function is fundamental to understanding the pathogenesis of the receptor-related disorders and to the development of new drug treatments. The long-term research goal of this laboratory is to elucidate the structural mechanisms of cys-loop receptor function and modulation using an interdisciplinary approach.

    Laboratory Accomplishments

    • Developed a novel highly efficient cloning technique to clone a PCR amplified cDNA fragment into any plasmid vector. This technique is purification free, ligation-independent, and sequence independent. It can be used for subcloning, chimeric cDNA construction, insertion, or deletion.
    • Discovered a novel mechanism of receptor desensitization: The decreased sensitivity of a cys-loop receptor is governed by the balance between coupling strength (of neurotransmitter binding domain and channel domain) and tightness of channel gate.
    • Identified several important amino acid residues in the binding pockets of GABA-A and GABA-C receptors responsible for selective antagonism by competitive antagonists of these two subtypes of GABA receptors.
    • Established a site-specific fluorescence reporting technique to detect the conformational change of GABA receptors in real time. This technique allows us to simultaneously record conformational change and channel function for the same oocyte expressing GABA receptors. With this technique, we are able to correlate conformational change of the receptor to channel function during channel activation and antagonism by competitive and noncompetitive antagonists.
    • Determined subunit stoichiometry of the major subtype of GABA-A receptors.
    • Developed a single oocyte-binding technique for an agonist-binding study and its correlation to channel function.
    • Provided the first experimental evidence that binding and gating are tightly coupled in the activation process of a ligand-gated ion channel.
    • Derived the binding affinities (not directly measurable) of a GABAA receptor at resting and open states.
    • Discovered that ultraviolet light has differential modulatory effects on the GABAA and GABAC receptors.
    • Provided the first direct evidence for the cyclic model of the GABAA receptor desensitization kinetics.
    • Adapted the site-specific fluorescence technique to study the structural dynamics of ligand-gated ion channels.
    • Generated a complete model of the rho-1 GABAC receptor-binding pocket using the substituted cysteine accessibility method.
    • Identified an evolutionarily conserved allosteric network in the cys-loop family of ligand-gated ion channels using statistical covariance analyses.