title: Role of polyhydroxybutyrate in mitochondrial calcium uptake.
abstract: Polyhydroxybutyrate (PHB) is a biological polymer which belongs to the class of polyesters and is ubiquitously present in all living organisms. Mammalian mitochondrial membranes contain PHB consisting of up to 120 hydroxybutyrate residues. Roles played by PHB in mammalian mitochondria remain obscure. It was previously demonstrated that PHB of the size similar to one found in mitochondria mediates calcium transport in lipid bilayer membranes. We hypothesized that the presence of PHB in mitochondrial membrane might play a significant role in mitochondrial calcium transport. To test this, we investigated how the induction of PHB hydrolysis affects mitochondrial calcium transport. Mitochondrial PHB was altered enzymatically by targeted expression of bacterial PHB hydrolyzing enzyme (PhaZ7) in mitochondria of mammalian cultured cells. The expression of PhaZ7 induced changes in mitochondrial metabolism resulting in decreased mitochondrial membrane potential in HepG2 but not in U87 and HeLa cells. Furthermore, it significantly inhibited mitochondrial calcium uptake in intact HepG2, U87 and HeLa cells stimulated by the ATP or by the application of increased concentrations of calcium to the digitonin permeabilized cells. Calcium uptake in PhaZ7 expressing cells was restored by mimicking calcium uniporter properties with natural electrogenic calcium ionophore - ferutinin. We propose that PHB is a previously unrecognized important component of the mitochondrial calcium uptake system.
authors.affiliation: Department of Physiology and Biophysics, Dalhousie University, Halifax, NS B3H 4R2, Canada.
authors.forename: Matthew
authors.initials: M
authors.lastname: Smithen
authors.forename: Pia A
authors.initials: PA
authors.lastname: Elustondo
authors.forename: Robert
authors.initials: R
authors.lastname: Winkfein
authors.forename: Eleonora
authors.initials: E
authors.lastname: Zakharian
authors.forename: Andrey Y
authors.initials: AY
authors.lastname: Abramov
authors.forename: Evgeny
authors.initials: E
authors.lastname: Pavlov
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002265:Carboxylic Ester Hydrolases / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D002470:Cell Survival; D005260:Female; D006367:HeLa Cells; D056945:Hep G2 Cells; D006801:Humans; D006885:Hydroxybutyrates / Q000378:metabolism*; D053078:Membrane Potential, Mitochondrial / Q000502:physiology; D008928:Mitochondria / Q000378:metabolism*; D011091:Polyesters / Q000378:metabolism*; D000091402:Prohibitins; D014162:Transfection; D000094122:Polyhydroxybutyrates
chemical_list: D001426:Bacterial Proteins; D002118:Calcium; D002265:Carboxylic Ester Hydrolases; D006885:Hydroxybutyrates; D011091:Polyesters; D000091402:Prohibitins; C000717328:PHB protein, human; C003182:poly-beta-hydroxybutyrate; D000094122:Polyhydroxybutyrates; C438011:PHAZ7 protein, Paucimonas lemoignei
keywords: Calcium; Inorganic polyphosphate; Mitochondria; PhaZ7; Poly-3-hydroxybutyrate