Structural and functional characterization of uncoupling proteins: Alkylsulfonates as probes of UCP transport mechanism
| Authors | |
|---|---|
| Year of publication | 2003 |
| Type | Article in Proceedings |
| Conference | Biophysics of the Genome |
| MU Faculty or unit | |
| Citation | |
| Field | Biochemistry |
| Keywords | uncoupling protein |
| Description | The mechanism of fatty acid-dependent uncoupling by mitochondrial uncoupling proteins (UCP) is still in debate. We have hypothesized that the anionic fatty acid head group is translocated by UCP, and the proton is transported electroneutrally in the bilayer by flip-flop of the protonated fatty acid. Alkylsulfonates are useful as probes of the UCP transport mechanism. They are analogues of fatty acids, and they are transported by UCP1, UCP2 and UCP3. Alkylsulfonates cannot be protonated because of their low pKa; consequently, they cannot catalyze electroneutral proton transport in the bilayer and cannot support uncoupling by UCP. We report that propranolol forms permeant ion pairs with the alkylsulfonates, thereby removing this restriction. Because a proton is transported with the neutral ion pair, the sulfonate is able to deliver protons across the bilayer, behaving as if it were a fatty acid. When ion pair transport is combined with UCP1, we now observe electrophoretic proton transport and uncoupling of brown adipose tissue mitochondria. These experiments confirm that the proton transport of UCP-mediated uncoupling takes place in the lipid bilayer and not through UCP itself. Thus, UCP1, like other members of its gene family, translocates anions and does not translocate protons. |
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