Neurobiology

Gary Yellen, Ph.D.

Professor of Neurobiology
Director of the Program in Neuroscience

Molecular Physiology of Ion Channels
All electrical signaling in the nervous system is controlled by ion channels, a class of membrane proteins that form pores through the membrane. Charged ions such as sodium, potassium and calcium pass through ion channels and carry an electrical current. The channels themselves are regulated, so that the pores are only open when the proper chemical or electrical signal is present, and only certain ions can pass through a particular kind of channel. By understanding how channels open and close and how they are regulated, we define the repertoire of molecular changes used by neurons when they signal, sense, and learn.

My laboratory uses single channel biophysics and directed mutagenesis to relate ion channel function to structure. Our studies are focused primarily on voltage-activated potassium channels. By systematic mutagenesis, we identified the region of the potassium channel protein that lines the pore through which ions cross the membrane, and the parts of the pore that change during opening and closing. In conjunction with our biophysical studies on the mechanisms of K+ channel inactivation and blockade, these discoveries put us in a position to learn about (and manipulate) the basic mechanism of channel gating at the level of individual amino acids. Another strategy we use is to introduce individual cysteine residues into the channel protein; these cysteines serve as targets for chemical modification and for metal binding. Our ability to modify the introduced cysteines in different conformational states gives specific information about the functional motions of the protein. These methods are also being applied to elucidate the unusual gating of pacemaker channels, which are important generators of rhythmic electrical behavior in the heart and brain.

A new direction in the lab is work on a remarkably effective but poorly understood therapy for epilepsy – the ketogenic diet. Used mainly for the many patients with drug-resistant epilepsy, this high fat, very low carb diet produces a dramatic reduction or elimination in seizures for most patients. We are investigating the possible role of metabolically-sensitive K+ channels (KATP channels) in the mechanism of the diet, and learning about their basic role in neuronal firing.

Figure Legend: The "bent S6" model for voltage-gated (Kv) channels (right), compared with the inner helices of KcsA (left). For Kv channels, the S6 segments are shown as two helices with an intervening bend, hypothesized to occur in the vicinity of the two prolines at positions 473 and 475. The intracellular entryway is at the bottom, and the bend produces a broad vestibule just below the bundle crossing. The hypothetical position of the intersubunit bridges Cys476-Cd2+-His486 are shown for the Kv channels (the cysteine sulfur is shown as a yellow ball, Cd2+ as a cyan sphere, and the histidine imidazole ring as a blue pentagon). Cd2+ bridging of these two residues can lock the Kv channel in the open state (Holmgren et al., 1998). For comparison, cysteine and histidine have been shown at the analogous positions in KcsA. This figure was derived from the KcsA structure solved by Rod MacKinnon's lab and from an exploratory molecular model of the Kv structure. (From del Camino et al., 2000; see also del Camino and Yellen, 2001, and Webster et al., 2004).