title: Mitofilin is a transmembrane protein of the inner mitochondrial membrane expressed as two isoforms.
abstract: Mitofilin, also known as heart muscle protein, is a recently identified mitochondrial protein. We have isolated two human cDNAs that encode different isoforms of mitofilin. Using reverse PCR, we provide evidence that both isoforms are derived by alternative splicing and encode two proteins of 88 and 90 kDa that are detected in immunoblot analyses with mitofilin-specific antibodies. Immunofluorescence microscopy, fractionating of human osteosarcoma cells, and protease protection experiments with isolated mitochondria and mitoplasts indicate that mitofilin is an integral membrane protein of the inner mitochondrial membrane. 35S-labeled mitofilin is transported into isolated yeast mitochondria in a reaction that depends on the membrane potential across the inner mitochondrial membrane (delta psi). During mitochondrial in vitro import, mitofilin is proteolytically processed to the mature protein that is also detected in cellular fractions, indicating that the amino-terminal leader sequence is removed. Sequence analysis and our results suggest that mitofilin is anchored in the inner mitochondrial membrane with an amino-terminal transmembrane domain, while the majority of the protein is extruding into the intermembrane space.
authors.affiliation: Faculty of Chemistry, Department of Biochemistry, University of Bielefeld, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Gieffers
authors.forename: F
authors.initials: F
authors.lastname: Korioth
authors.forename: P
authors.initials: P
authors.lastname: Heimann
authors.forename: C
authors.initials: C
authors.lastname: Ungermann
authors.forename: J
authors.initials: J
authors.lastname: Frey
mesh_terms: D000595:Amino Acid Sequence; D001859:Bone Neoplasms / Q000473:pathology; D018076:DNA, Complementary / Q000235:genetics; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D024101:Mitochondrial Proteins; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000378:metabolism; D010006:Osteoblasts / Q000378:metabolism; D012516:Osteosarcoma / Q000473:pathology; D016133:Polymerase Chain Reaction; D021382:Protein Sorting Signals / Q000378:metabolism; D012326:RNA Splicing
chemical_list: D018076:DNA, Complementary; C088548:IMMT protein, human; D024101:Mitochondrial Proteins; D009124:Muscle Proteins; D009363:Neoplasm Proteins; D021382:Protein Sorting Signals