Mitochondrial protein import

We propose that hydrophobic 'assistant' sequences can increase the efficiency of import

Franz-Ulrich Hartl; Nikolaus Pfanner; Donald W. Nicholson; Walter Neupert

2003

Scholarcy highlights

  • A great deal of new information on how mitochondria import proteins has been gathered over the last few years
  • It has been demonstrated that protein transport across the membranes of mitochondria, chloroplasts, the endoplasmic reticulum, peroxisomes, and across the plasma membrane of Escherichia coil all require ATP and can occur posttranslationaily
  • The specific binding of the ADP/ATP carrier precursor to the mitochondrial surface required a cytosolic component which was present in rabbit reticulocyt¢ lysate and which interacted with isolated mitochondria
  • Substitution of the arginine at position 23 of the oraithine transcarbamoylase precursor with glycine resulted in a complete loss of targeting function ; when arginine 23 was substituted with an amino acid residue supporting the formation of a-helical structure, the modified precursor was imported into mitochondria
  • The remaining import, is of low efficiency and is less stwxific, allowing precursor proteins with non-mitochondriai targeting sequences to be imported. This bypassimport still reflects several obfigatory mechanistic features for translocation of proteins into mitochondria; precursors must have the ability to insert into the outer mitochondrial membrane which may be facilitated by an amphiphilic structure of the signal peptide; and precursors enter the inner membrane in a manner that is dependent on the mitochondrial membrane potential, which probably exerts an electrophoretic effect on the positively charged signal sequence
  • We propose that a factor, which might be an unfoldase as recently proposed, acts together with nucleoside triphosphates to keep precursor proteins in an import-competent conformation
  • This bypassimport still reflects several obfigatory mechanistic features for translocation of proteins into mitochondria; precursors must have the ability to insert into the outer mitochondrial membrane which may be facilitated by an amphiphilic structure of the signal peptide; and precursors enter the inner membrane in a manner that is dependent on the mitochondrial membrane potential, which probably exerts an electrophoretic effect on the positively charged signal sequence

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