Frederick J. Sigworth PhD

Professor of Cellular and Molecular Physiology and of Biomedical Engineering

Research Interests

Cell Physiology; Electron Microscopy; Electrophysiology; Ion Channel; Mathematical Model; Patch Clamp; Potassium Channel; Protein Structure; Sodium Channel; Voltage Gated Channel; Xenopus Oocyte


Research Summary

Ion channels act as molecular transducers, responding to chemical, mechanical, or electrical stimuli by opening a pore to allow ionic current to flow. Work in my laboratory seeks to clarify the transduction mechanisms of channel proteins. We use single-particle imaging in electron cryo-microscopy to obtain three-dimensional structures of channel proteins. To this end we are developing new computational and experimental methods for imaging membrane proteins in membranes. To study function we use patch-clamp recordings for the sensitive measurement of ion channel currents and collaborate with colleagues in Yale engineering departments to advance this technology as well.

Extensive Research Description

My research work centers on the structure and function of ion channels, which are membrane proteins that selectively control the passage of ions across cell membranes. The activity of ion channels is central to very many physiological processes, including synaptic transmission and impulse propagation in the nervous system, the control of cardiac function and vascular resistance, salt and water transport in epithelia, and the control of hormone secretion.

Central to the understanding of ion channel function is the characterization of the stochastic 'gating' behavior of single channels. We are particularly interested in the 'voltage sensor' of voltage-gated potassium channels, and how it couples the transmembrane potential to channel gating. Towards an understanding of this protein structure, we are pursuing studies using electron cryo-microscopy (cryo-EM) of voltage-gated channel proteins. Electron microscopes have sufficient resolution to provide atomic-detail images, but 'radiation damage' by the electron beam precludes structure determination from a single molecule. Instead, images from many individual protein molecules must be combined to yield even low-resolution structural information. Working with potassium channels reconstituted into lipid vesicles, we use novel specimen substrates and 'single-particle' image processing methods to obtain the three-dimensional structure of these proteins.

The process of obtaining 3D protein structures from electron micrographs is a very interesting mathematical problem. We are pursuing new approaches to make this process more reliable and able to work on smaller protein particles (like ion channels) than those investigated in the past.



Selected Publications

  • Wang L and Sigworth FJ. Structure of the BK potassium channel in a lipid membrane from electron cryomicroscopy. Nature, 461(7261):292-5, 2009.
  • Singer A, Coifman RR, Sigworth FJ, Chester DW, Shkolnisky Y. Detecting consistent common lines in cryo-EM by voting. J Struct Biol. 2009 Nov 17. [Epub ahead of print]
  • Weerakoon, P.; Sigworth, F.; Culurciello, E.. Integrated patch-clamp biosensor for high-density screening of cell conductance. Electronics Letters, 44:81-82, 2008.
  • Wang L, Ounjai P, Sigworth FJ. Streptavidin crystals as nanostructured supports and image-calibration references for cryo-EM data collection. J Struct Biol, epub, 2008.
  • Wang L, Bose PS, Sigworth FJ. Using cryo-EM to measure the dipole potential of a lipid membrane. PNAS, 103:18528-33, 2006.
  • Giraldez, T, Hughes TE, Sigworth FJ. Generation of functional fluorescent BK channels by random insertion of GFP variants. J Gen Physiol, 126:429-38, 2005.

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