Members of the CIC family orchestrate the movements of chloride necessaryfor proper neuronal, muscuiar, cardiovascular, and epithelial function. Although certain eukaryotic CICchannels have boenwell characterized functionally, we remain in the dark about their detailed structures. Conversely, the structures of two prokaryotic CIC homologs were determined by x-ray crystallography, but we know little about their function. The high sequence identity between core invariant segments of prokaryotic and eukaryotic CICs argues for a shared structural scaffold, but the low (15-20%)overall identity also indicate>5 that these families; differ in significant details. A striking functional correlate of the structural differences is the recent finding that CIC-ec1, an E. coli CIC, is not a chloride channel but a chloride-proton antiporter. Thus, the CIC family straddles an evolutionary cusp between these two different transport mechanisms. Our long-range goal is to determine how proton and chloride movement are coupled in CIC-ec1 and how this relates to proton- and chloride-activation of voltage-dependent gating in CIC-0. This work will shed light on the general mechanism of chloride permeation in the CIC family members, and will be essential for understanding the diverse physiology and pathophysiology seen amongst the CIC family members.
In Specific Aim 1, we will test models of chloride-proton antiport using bilayer recordings and flux assaystogether withsite-directed mutagenesis. Important technical developments include methods for obtaining oriented transporters, andthe use of a high-throughput fluorescence-based transport assay to screenfor specific inhibitors.
In Specific aim 2, we will mapthe intracellular vestibule of CIC-0 using cysteine scanning mutagenesis. We will probe gating conformational changes by examining rates of cysteine modification under different conditions. Finally,we will analyze voltage- and proton-dependent gating at the single-channel level for mutations that cause significant changes in gating. Together, these studies will offer new insights into the functional relationships between channels and transporters.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
3R01GM070773-05S1
Application #
7893424
Study Section
Biophysics of Synapses, Channels, and Transporters Study Section (BSCT)
Program Officer
Chin, Jean
Project Start
2009-08-31
Project End
2010-07-31
Budget Start
2009-08-31
Budget End
2010-07-31
Support Year
5
Fiscal Year
2009
Total Cost
$137,751
Indirect Cost
Name
Stanford University
Department
Biophysics
Type
Schools of Medicine
DUNS #
009214214
City
Stanford
State
CA
Country
United States
Zip Code
94305
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