Date of Degree
PhD (Doctor of Philosophy)
Molecular Physiology and Biophysics
Christopher A. Ahern
The pedigree of voltage-gated sodium channels spans the millennia from eukaryotic members that initiate the action potential firing in excitable tissues to primordial ancestors that act as enviro-protective complexes in bacterial extremophiles. Eukaryotic sodium channels (eNavs) are central to electrical signaling throughout the cardiovascular and nervous systems in animals and are established clinical targets for the therapeutic management of epilepsy, cardiac arrhythmia and painful syndromes as they are inhibited by local anesthetic compounds. Alternatively, bacterial voltage-gated sodium channels (bNavs) likely regulate the survival response against extreme pH conditions, electrophiles and hypo-osmotic shock and may represent a founder of the voltage-gated cation channel family. Despite apparent differences between eNav and bNav channel physiology, gating and gene structure, the discovery that bNavs are amenable to crystallographic study opens the door for the possibility of structure-guided rational design of the next generation of therapeutics that target eNavs. Here I summarize the gating behavior of a bacterial channel NaChBac and discuss mechanisms of local anesthetic inhibition in light of the growing number of bNav structures. Also, an interesting novel observation on cross-lineage modulation of NaChBac by eNav beta subunit is reported. This auxiliary subunit modulation is isoform specific and I show the discrete effects of each isoforms on NaChBac, with functional and biochemical analysis. I also report a novel mutation that alters inactivation kinetic drastically and a possible mechanism of NaChBac inactivation is discussed.
We have many ions in our body. Movement of ions in and out of cells mediates the generation of electrical signals in our nerves and heart, controlling the physiological processes like electrical signal transduction through our spine or regulating the normal heartbeat. Voltage-gated sodium channels are the main players of initiating and propagating this electrical stimulus, thereby any defects in these channels can lead to serious clinical conditions. Electrical rhythm disorders, such as epilepsy and arrhythmia, are treated with drugs that are made to inhibit hyperactive sodium channels. One of the proven drug targets of such clinical conditions are the non-conducting, inactivated sodium channels. However, we know little about the molecular mechanism of how sodium channels enter this non-conducting state, nor do we know where these drugs exactly bind to inhibit the uncontrolled activity of the sodium channels. The focus of my thesis is to understand the biophysical and pharmacological properties of voltage-gated sodium channel from bacteria that we have the structure of; with the hope that the structure-function understanding will be an asset to designing the next generation therapeutic agents that will acutely target the defective sodium channels. We also explore the conserved modulatory effects of sodium channel auxiliary subunits on the bacterial channel. Albeit the separation of millions of years between the evolution of mammals and bacteria, mammalian sodium channel auxiliary subunit altered the biophysical properties of the bacterial sodium channel, in a similar way to the mammalian channels. Continued research is needed to broaden our understanding of the voltage-gated sodium channels and its incredibly important roles in human physiology.
publicabstract, bacterial sodium channel, biophysics, ion channels, pharmacology
x, 113 pages
Includes bibliographical references (pages 100-113).
Copyright 2014 So Ra Lee