title: Mitochondrial protein import: recognition of internal import signals of BCS1 by the TOM complex.
abstract: BCS1, a component of the inner membrane of mitochondria, belongs to the group of proteins with internal, noncleavable import signals. Import and intramitochondrial sorting of BCS1 are encoded in the N-terminal 126 amino acid residues. Three sequence elements were identified in this region, namely, the transmembrane domain (amino acid residues 51 to 68), a presequence type helix (residues 69 to 83), and an import auxiliary region (residues 84 to 126). The transmembrane domain is not required for stable binding to the TOM complex. The Tom receptors (Tom70, Tom22 and Tom20), as determined by peptide scan analysis, interact with the presequence-like helix, yet the highest binding was to the third sequence element. We propose that the initial recognition of BCS1 precursor at the surface of the organelle mainly depends on the auxiliary region and does not require the transmembrane domain. This essential region represents a novel type of signal with targeting and sorting functions. It is recognized by all three known mitochondrial import receptors, demonstrating their capacity to decode various targeting signals. We suggest that the BCS1 precursor crosses the TOM complex as a loop structure and that once the precursor emerges from the TOM complex, all three structural elements are essential for the intramitochondrial sorting to the inner membrane.
authors.affiliation: Institut für Physiologische Chemie der Universität München, D-81377 Munich, Germany.
authors.forename: Tincuta
authors.initials: T
authors.lastname: Stan
authors.forename: Jan
authors.initials: J
authors.lastname: Brix
authors.forename: Jens
authors.initials: J
authors.lastname: Schneider-Mergener
authors.forename: Nikolaus
authors.initials: N
authors.lastname: Pfanner
authors.forename: Walter
authors.initials: W
authors.lastname: Neupert
authors.forename: Doron
authors.initials: D
authors.lastname: Rapaport
mesh_terms: D000074183:ATPases Associated with Diverse Cellular Activities; D000818:Animals; D001665:Binding Sites / Q000502:physiology; D001667:Binding, Competitive / Q000502:physiology; D005656:Fungal Proteins / Q000737:chemistry; D046911:Macromolecular Substances; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins; D051379:Mice; D008928:Mitochondria / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D024101:Mitochondrial Proteins; D018832:Molecular Chaperones / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D009492:Neurospora crassa; D019151:Peptide Library; D011485:Protein Binding / Q000502:physiology; D017510:Protein Folding; D017434:Protein Structure, Tertiary / Q000502:physiology; D021381:Protein Transport / Q000502:physiology; D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013329:Structure-Activity Relationship; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics
chemical_list: C472685:BCS1 protein, S cerevisiae; D005656:Fungal Proteins; D046911:Macromolecular Substances; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D024101:Mitochondrial Proteins; D018832:Molecular Chaperones; D019151:Peptide Library; D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; C489350:TOM20 protein, S cerevisiae; C090857:TOM22 protein, S cerevisiae; C489039:TOM70 protein, S cerevisiae; C489997:Tomm20 protein, mouse; D013762:Tetrahydrofolate Dehydrogenase; D000074183:ATPases Associated with Diverse Cellular Activities