Choline head groups stabilize the matrix loop regions of the ATP/ADP carrier ScAAC2.
ATP/ADP carriers (AACs) are essential to the cell as they exchange ATP produced in mitochondria for cytosolic ADP. Monoclonal antibodies against the isoform 2 of Saccharomyces cerevisiae AAC (ScAAC2) were used to probe the accessibility of the matrix loops 1 and 3 depending on the environment of the carrier. In mitochondrial membranes ScAAC2 was not recognized, whereas in dodecylmaltoside the antibodies bound to the carrier, suggesting that the epitopes are hidden in the native environment. Exposure of the epitopes by detergents was reversed by reconstitution of the carrier in phospholipids or by exchanging with detergents having a choline or a trimethylammonium head group. Circular dichroism spectroscopy on peptides representing the C-terminal regions of all three matrix loops showed that only phosphocholine detergents induced a structural reorganization. Since in addition phosphatidylcholine was found to be tightly associated with the purified carrier, the matrix loop regions are likely to be associated to the membrane by phosphatidylcholine.
Panneels
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European Molecular Biology Laboratory, 1 MeyerhofStrasse, Heidelberg 69112, Germany.
Schüssler
Ute
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Costagliola
Sabine
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Sinning
Irmgard
I
D000595:Amino Acid Sequence; D000908:Antibodies, Fungal; D000911:Antibodies, Monoclonal; D000946:Antigens, Fungal / Q000737:chemistry / Q000235:genetics; D002794:Choline / Q000737:chemistry; D002942:Circular Dichroism; D003902:Detergents; D018604:Epitope Mapping; D000226:Mitochondrial ADP, ATP Translocases / Q000737:chemistry* / Q000276:immunology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010713:Phosphatidylcholines; D011487:Protein Conformation; D012441:Saccharomyces cerevisiae / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000276:immunology
D000908:Antibodies, Fungal; D000911:Antibodies, Monoclonal; D000946:Antigens, Fungal; D003902:Detergents; C112225:PET9 protein, S cerevisiae; D010713:Phosphatidylcholines; D029701:Saccharomyces cerevisiae Proteins; D000226:Mitochondrial ADP, ATP Translocases; D002794:Choline