| Members of the DEG/ENaC family are homologous proteins with two transmembrane domains, cytoplasmic N- and C-termini and a large extracellular loop. This family was discovered in 1990 with the identification and partial cloning of DEG-1, a protein responsible for neurodegeneration in Caenorhabditis elegans. A few years later, a DEG/ENaC protein from rat colon was shown to form amiloride-sensitive Na+ channels; this finding led to the realization that DEG/ENaC proteins composed a novel family of ion channels. Since then, DEG/ENaC proteins have been shown to participate in a variety of physiologic processes, including epithelial electrolyte transport, neurotransmission, and the perception of touch, position, salty taste and perhaps pain.; The studies described in this dissertation were designed to address a few fundamental questions regarding DEG/ENaC channel structure and function. In the first part (Chapter 1), I tested the hypothesis that DEG/ENaC proteins assemble to form multimeric ion channels. I also asked which portion of an individual DEG/ENaC protein (or subunit) mediates intersubunit interactions.; In the second part of this dissertation (Chapters 2–4), I investigated the mechanism by which extracellular ligands and certain mutations activate some neuronal DEG/ENaC channels. I also focused on effect of amiloride, a drug which blocks all known DEG/ENaC channels, and described how amiloride can stimulate channel activity in some situations. Finally, I studied the pore structure of a DEG/ENaC channel and examined the similarity of DEG/ENaC channels to other classes of ion channels.; In the last part (Chapter 5), I describe the molecular cloning and characterization of two novel DEG/ENaC proteins from Drosophila melanogaster. These proteins are the first identified Drosophila family members and represent a novel branch of the DEG/ENaC family. Despite their sequence similarity, these proteins likely perform distinct physiologic functions: one is a neuronal protein that likely functions in mechanosensation; the other is a non-neuronal Na+ channel that may play a role in early development. |
