Exploring the Biophysical Properties of Human Uncoupling Proteins: A Search for their Physiological Roles in the Central Nervous System

Tuan Hoang,Matthew D Smith,Masoud Jelokhani-Niaraki

doi:10.1016/j.bpj.2011.11.3409

Tuan Hoang, Matthew D Smith + Show 1 more

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https://doi.org/10.1016/j.bpj.2011.11.3409

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Journal: Biophysical Journal	Publication Date: Jan 1, 2012
License type: elsevier-specific: oa user license

Affiliation: Wilfrid Laurier University, University of Guelph

Abstract

Expressed in brown adipose tissues (BAT), uncoupling protein-1 (UCP1) facilitates proton transport across the inner mitochondrial membrane, reducing the membrane potential and rate of ATP synthesis. The excessive proton flux carried by UCP1 produces heat in BAT. Three other UCP homologues (UCP2, UCP4 and UCP5) are expressed in the central nervous system (CNS), but their physiological functions are not well understood. The goal of this study is to explore the biophysical properties of neuronal UCPs reconstituted in liposomes to gain an insight into the specific roles of these proteins in the CNS. The three neuronal UCPs were recombinantly expressed, purified and reconstituted in lecithin liposomes (with and without the supplement of 2.5 mol% cardiolipin (CL)). Ion transport assays (proton and chloride) for reconstituted UCPs were developed using anion-sensitive fluorescent probes. All neuronal UCPs displayed proton transport across the membrane with characteristics similar to the archetypical protein UCP1, which is activated by fatty acids and inhibited by purine nucleotides. UCP2 and UCP4 showed high alpha-helical contents in liposomes and conducted chloride. Ion transport of UCPs 4 and 5 was reported for the first time in this study. In addition, it was observed that the mitochondrial lipid CL induced changes in conformation and ion transport properties of reconstituted UCPs. A hypothetical interaction mechanism of UCPs and CL was drawn from the experimental results and molecular modelling. Overall, this study provides the groundwork on the conformation and ion transport properties of neuronal UCPs in liposomes, and emphasizes the crucial role of cardiolipin in UCPs’ structure and function. Understanding the structure-function relationships of neuronal UCPs will be essential in shedding light on their potential roles in protection against neurodegenerative diseases in the CNS.

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