The preprotein translocase of the mitochondrial inner membrane: function and evolution

• Published in: Journal of molecular biology 1999-02, Vol.286 (1), p.105-120
• Main Authors: Rassow, Joachim, Dekker, Peter J.T, van Wilpe, Sandra, Meijer, Michiel, Soll, Jürgen
• Format: Article
• Language: English
• Subjects: Adenosine Triphosphatases - physiology; Amino Acid Sequence; Animals; Bacterial Proteins - physiology; Carrier Proteins - metabolism; Escherichia coli Proteins; HSP70 Heat-Shock Proteins - metabolism; Intracellular Membranes - enzymology; LivH; Membrane Proteins - chemistry; Membrane Proteins - metabolism; Membrane Transport Proteins; mitochondria; Mitochondria - enzymology; Mitochondria - metabolism; Mitochondrial Membrane Transport Proteins; Molecular Sequence Data; mtHsp70; OEP16; Plants; PRAT family; Repressor Proteins; Saccharomyces cerevisiae Proteins; SEC Translocation Channels; Sequence Homology, Amino Acid; Tim proteins
• ISSN: 0022-2836; 1089-8638
• DOI: 10.1006/jmbi.1998.2455

Growing mitochondria acquire most of their proteins by the uptake of mitochondrial preproteins from the cytosol. To mediate this protein import, both mitochondrial membranes contain independent protein transport systems: the Tom machinery in the outer membrane and the Tim machinery in the inner membrane. Transport of proteins across the inner membrane and sorting to the different inner mitochondrial compartments is mediated by several protein complexes which have been identified in the past years. A complex containing the integral membrane proteins Tim17 and Tim23 constitutes the import channel for preproteins containing amino-terminal hydrophilic presequences. This complex is associated with Tim44 which serves as an adaptor protein for the binding of mtHsp70 to the membrane. mtHsp70, a 70 kDa heat shock protein of the mitochondrial matrix, drives the ATP-dependent import reaction of the processed preprotein after cleavage of the presequence. Preproteins containing internal targeting information are imported by a separate import machinery, which consists of the intermembrane-space proteins Tim9, Tim10, and Tim12, and the inner membrane proteins Tim22 and Tim54. The proteins Tim17, Tim22, and Tim23 have in common a similar topology in the membrane and a homologous amino acid sequence. Moreover, they show a sequence similarity to OEP16, a channel-forming amino acid transporter in the outer envelope of chloroplasts, and to LivH, a component of a prokaryotic amino acid permease, defining a new PRAT-family of pr eprotein and a mino acid t ransporters.