Cardiolipin regulates the activity of the reconstituted mitochondrial calcium uniporter by modifying the structure of the liposome bilayer.
Reconstitution of mitochondrial calcium transport activity requires the incorporation of membrane proteins into a lipidic ambient. Calcium uptake has been measured previously using Cytochrome oxidase vesicles. The enrichment of these vesicles with cardiolipin, an acidic phospholipid that is found only in the inner mitochondrial membrane of eukaryotic cells, strongly inhibits calcium transport, in remarkable contrast with the activation effect that cardiolipin exerts upon other mitochondrial transporters and enzymes. The relation of the inactivation of calcium transport to the physical state of the bilayer was studied by following the polarization changes of 1,6-diphenyl-1,3,5-hexatriene (DPH) and by flow cytometry in the cardiolipin-enriched liposomes with incorporated mitochondrial solubilized proteins. Non-bilayer molecular arrangements in the cardiolipin-supplemented liposomes, detected by flow cytometry, may produce the fluidity changes observed by fluorescence polarization of DPH. Fluidity changes correlate with the abolition of calcium uptake, but have no effect on the establishment of a membrane potential in the vesicles required for calcium transport activity. Changes in the membrane structure and uniporter function are observed in the combined presence of cardiolipin and calcium leading to a modified lipid configuration.
Zazueta
C
C
Departamento de Bioquímica, Instituto Nacional de Cardiología Ignacio Chávez, Juan Badiano No.1, México 04080, D.F., México. czazuetam@hotmail.com
Ramírez
J
J
García
N
N
Baeza
I
I
D002118:Calcium / Q000737:chemistry* / Q000378:metabolism; D015220:Calcium Channels; D002135:Calcium-Binding Proteins / Q000737:chemistry* / Q000378:metabolism; D002308:Cardiolipins / Q000737:chemistry* / Q000378:metabolism; D002457:Cell Extracts / Q000737:chemistry; D003576:Electron Transport Complex IV / Q000737:chemistry; D005434:Flow Cytometry / Q000379:methods; D005454:Fluorescence Polarization / Q000379:methods; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D008081:Liposomes / Q000737:chemistry* / Q000378:metabolism; D008928:Mitochondria / Q000737:chemistry* / Q000378:metabolism; D008968:Molecular Conformation; D010713:Phosphatidylcholines; D010743:Phospholipids / Q000737:chemistry; D013329:Structure-Activity Relationship; D013696:Temperature
D015220:Calcium Channels; D002135:Calcium-Binding Proteins; D002308:Cardiolipins; D002457:Cell Extracts; D008051:Lipid Bilayers; D008081:Liposomes; D010713:Phosphatidylcholines; D010743:Phospholipids; C034703:mitochondrial calcium uniporter; C024990:asolectin; D003576:Electron Transport Complex IV; D002118:Calcium