Edwin Chapman

Membrane trafficking and fusion in neurons

Our laboratory uses quantitative biophysical approaches to address fundamental questions regarding membrane traffic and fusion in neurons. A major focus is to understand how synaptic vesicles fuse with the presynaptic plasma membrane to mediate synaptic transmission. We address these questions both using both bottom-up and top-down approaches. The former relies on the reconstitution of the proteins that catalyze fusion, and these efforts hinge on the combined use of a wide variety of tools, including nanodiscs and planar lipid bilayer electrophysiology to interrogate nascent fusion pores with µsec time resolution, DNA nanostructures to control the reconstitution of membrane proteins, giant unilamellar vesicles to study the membrane sculpting activity of release proteins, and atomic force/electron tunneling/electron microscopy to visualize protein and membrane structure. The latter, top-down approach involves the perturbation of proteins within intact cells. Since many of the proteins under study have long half-lives, and since synapses are highly plastic, we have innovated new methods to acutely inactivate proteins of interest. We then interrogate synapses using electrophysiological and optical approaches. For example, we are currently using fluorescent sensors that directly report the release of neurotransmitters. The goal of these biophysical studies is to elucidate the nanomechanics of the fusion reaction.

Figure legend: Nanodisc (ND)-black lipid membrane BLM) set-up and typical recording of fusion pore dynamics. (a) The v-SNARE (synaptobrevin 2 or syb2), reconstituted in a ND, interacts with the t-SNAREs present in the BLM to form a fusion pore, as shown in the illustration. (b) Traces of single pores at ΔΨ = −50 mV for ND bearing ~ 5 copies of syb2. Closed (C) and open (O) states are indicated, along with the respective currents.

Lab website

Neuroscience Department Faculty website

HHMI website

Representative publications:

Bao, H. Das, D. Courtney, N. Jiang, Y. Briguglio, J. Lou, X. Roston, D. Cui, Q. Chanda B. & Chapman, E.R. (2018). Dynamics and number of Trans-SNARE complexes determine nascent fusion pore properties. Nature 554(7691): 260-263.  PMID: 29420480  [PMCID in progress]

Bao, H., Goldschen-Ohm, M.O., Jeggle, P., Chanda, B., Edwardson, J.M.  & Chapman, E.R.. (2016). Exocytotic fusion pores are composed of both lipids and proteins. Nature Struct. Mol. Biol. 23(1): 67-73. PMCID: PMC4756907. Cover/featured article.

 *Bai, H., *Xue, R., Zhang, L., Yethiraj, A., Cui, Q. and Chapman, E.R. (2016). Different states of synaptotagmin control evoked versus spontaneous synaptic vesicle exocytosis. Nature Comm. 7: 10971. PMCID: PMC4804166. *equal contribution

Evans, C.S., Ruhl, D. & Chapman, E.R.. (2015). An engineered metal sensor tunes the kinetics of synaptic transmission. J. Neuroscience 35(34): 11769-79. PMCID: PMC4549396