title: A biophysical study on molecular physiology of the uncoupling proteins of the central nervous system.
abstract: Mitochondrial inner membrane uncoupling proteins (UCPs) facilitate transmembrane (TM) proton flux and consequently reduce the membrane potential and ATP production. It has been proposed that the three neuronal human UCPs (UCP2, UCP4 and UCP5) in the central nervous system (CNS) play significant roles in reducing cellular oxidative stress. However, the structure and ion transport mechanism of these proteins remain relatively unexplored. Recently, we reported a novel expression system for obtaining functionally folded UCP1 in bacterial membranes and applied this system to obtain highly pure neuronal UCPs in high yields. In the present study, we report on the structure and function of the three neuronal UCP homologues. Reconstituted neuronal UCPs were dominantly helical in lipid membranes and transported protons in the presence of physiologically-relevant fatty acid (FA) activators. Under similar conditions, all neuronal UCPs also exhibited chloride transport activities that were partially inhibited by FAs. CD, fluorescence and MS measurements and semi-native gel electrophoresis collectively suggest that the reconstituted proteins self-associate in the lipid membranes. Based on SDS titration experiments and other evidence, a general molecular model for the monomeric, dimeric and tetrameric functional forms of UCPs in lipid membranes is proposed. In addition to their shared structural and ion transport features, neuronal UCPs differ in their conformations and proton transport activities (and possibly mechanism) in the presence of different FA activators. The differences in FA-activated UCP-mediated proton transport could serve as an essential factor in understanding and differentiating the physiological roles of UCP homologues in the CNS.
authors.affiliation: Department of Chemistry and Biochemistry, Wilfrid Laurier University, Waterloo, Ontario, Canada, N2L 3C5 Biophysics Interdepartmental Group, University of Guelph, Guelph, Ontario, Canada, N1G 2W1.
authors.forename: Tuan
authors.initials: T
authors.lastname: Hoang
authors.affiliation: Department of Chemistry and Biochemistry, Wilfrid Laurier University, Waterloo, Ontario, Canada, N2L 3C5.
authors.forename: Miljan
authors.initials: M
authors.lastname: Kuljanin
authors.affiliation: Department of Biology, Wilfrid Laurier University, Waterloo, Ontario, Canada, N2L 3C5 Biophysics Interdepartmental Group, University of Guelph, Guelph, Ontario, Canada, N1G 2W1.
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Smith
authors.affiliation: Department of Chemistry and Biochemistry, Wilfrid Laurier University, Waterloo, Ontario, Canada, N2L 3C5 Biophysics Interdepartmental Group, University of Guelph, Guelph, Ontario, Canada, N1G 2W1 mjelokhani@wlu.ca.
authors.forename: Masoud
authors.initials: M
authors.lastname: Jelokhani-Niaraki
mesh_terms: D002490:Central Nervous System / Q000378:metabolism; D006801:Humans; D007473:Ion Channels / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017510:Protein Folding; D017433:Protein Structure, Secondary
chemical_list: D007473:Ion Channels; D024101:Mitochondrial Proteins; D009419:Nerve Tissue Proteins
keywords: central nervous system (CNS); circular dichroism (CD) spectroscopy; fatty acid (FA); membrane protein folding; molecular association; proton transport; reconstitution; uncoupling proteins (UCPs)