The Golgi complex is present in every eukaryotic cell, from yeast to humans, and functions in posttranslational protein modifications and sorting of these molecules to post-Golgi destinations. Both processes require an acidic lumenal pH and transport of substrate and reactants into and out of the Golgi lumen. Endogenous ion channels are expected to be important for regulating the ionic environment within the Golgi lumen. This proposal is to isolate and characterize these endogenous ion channels of the Golgi complex and is a collaboration between two laboratories, one that studies ion channels and one that studies Golgi function. Single ion channel studies are now feasible because we have recently improved the isolation of a Golgi fraction from rat liver. We eliminated proteins transiting the Golgi and achieved a 400-700 fold enrichment of endogenous Golgi proteins. Ion channels in the enriched fraction have been incorporated into planar lipid bilayers. We named the most prevalent ion channel GOLAC1 (Golgi Anion Channel 1). This channel has novel properties and is modulated by pH on the lumenal surface. Two hypotheses are proposed for the function of the GOLAC 1: first, it provides counterions necessary for acidification of the Golgi lumen by an electrogenic H+ATPase and second, it removes phosphate (generated by glycosylation and sulfation) from the Golgi lumen. There are three specific aims. (1) Electrophysiologically characterize anion and cation channels of the Golgi. (2) Obtain peptide and cDNA sequence by enriching for channel activity with subfractionation of detergent- solubilized Golgi proteins. Proteins that enrich in parallel with channel activity will be identified using 2D-gel electrophoresis, mass spectrometry, and peptide sequencing. The cDNA identified will be expressed, purified, and confirmed to be a GOLAC in bilayer studies and a Golgi protein by immunofluorescence. (3) Study modulation of Golgi channels by candidate molecules and cell factors. From a clinical viewpoint, there are an increasing number of diseases classified as ion channelopathies. It is likely that some human diseases will be due to mutations of endogenous Golgi channels.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM059987-02
Application #
6387009
Study Section
Cell Development and Function Integrated Review Group (CDF)
Program Officer
Shapiro, Bert I
Project Start
2000-04-01
Project End
2003-03-31
Budget Start
2001-04-01
Budget End
2002-03-31
Support Year
2
Fiscal Year
2001
Total Cost
$372,032
Indirect Cost
Name
University of Colorado Denver
Department
Biology
Type
Schools of Medicine
DUNS #
065391526
City
Aurora
State
CO
Country
United States
Zip Code
80045
Thompson, Roger J; Akana, Hillary C S R; Finnigan, Claire et al. (2006) Anion channels transport ATP into the Golgi lumen. Am J Physiol Cell Physiol 290:C499-514
Nordeen, M H; Jones, S M; Howell, K E et al. (2000) GOLAC: an endogenous anion channel of the Golgi complex. Biophys J 78:2918-28