title: Import of cytochrome b2 to the mitochondrial intermembrane space: the tightly folded heme-binding domain makes import dependent upon matrix ATP.
abstract: Cytochrome b2 is synthesized as a precursor in the cytoplasm and imported to the intermembrane space of yeast mitochondria. We show here that the precursor contains a tightly folded heme-binding domain and that translocation of this domain across the outer membrane requires ATP. Surprisingly, it is ATP in the mitochondrial matrix rather than external ATP that drives import of the heme-binding domain. When the folded structure of the heme-binding domain is disrupted by mutation or by urea denaturation, import and correct processing take place in ATP-depleted mitochondria. These results indicate that (1) cytochrome b2 reaches the intermembrane space without completely crossing the inner membrane, and (2) some precursors fold outside the mitochondria but remain translocation-competent, and import of these precursors in vitro does not require ATP-dependent cytosolic chaperone proteins.
authors.affiliation: Biocenter, University of Basel, Switzerland.
authors.forename: B S
authors.initials: BS
authors.lastname: Glick
authors.forename: C
authors.initials: C
authors.lastname: Wachter
authors.forename: G A
authors.initials: GA
authors.lastname: Reid
authors.forename: G
authors.initials: G
authors.lastname: Schatz
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D001665:Binding Sites; D001693:Biological Transport, Active; D002451:Cell Compartmentation; D006418:Heme / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism*; D007770:L-Lactate Dehydrogenase / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D042844:L-Lactate Dehydrogenase (Cytochrome); D008928:Mitochondria / Q000378:metabolism*; D008954:Models, Biological; D010446:Peptide Fragments / Q000378:metabolism; D011489:Protein Denaturation; D017510:Protein Folding; D011498:Protein Precursors / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics / Q000378:metabolism; D014508:Urea / Q000494:pharmacology
chemical_list: D010446:Peptide Fragments; D011498:Protein Precursors; D011993:Recombinant Fusion Proteins; D006418:Heme; D000255:Adenosine Triphosphate; D014508:Urea; D007770:L-Lactate Dehydrogenase; D042844:L-Lactate Dehydrogenase (Cytochrome); D013762:Tetrahydrofolate Dehydrogenase