Biogenesis of mitochondrial porin: The import pathway

Abstract

Summary. We review here the present knowledge about the pathway of import and assembly of porin into mitochondria and compare it to those of other mitochondrial proteins. Porin, like all outer mitochondrial membrane proteins studied so far is made as a precursor without a cleavable 'signal' sequence; thus targeting information must reside in the mature sequence. At least part of this information appears to be located at the amino-terminal end of the molecule. Transport into mitochondria can occur post-translationally. In a first step, the porin precursor is specifically recognized on the mitochondrial surface by a protease sensitive receptor. In a second step, porin precursor inserts partially into the outer membrane. This step is mediated by a component of the import machinery common to the import pathways of precursor proteins destined for other mitochondrial subcompartments. Finally, porin is assembled to produce the functional oligomeric form of an integral membrane protein wich is characterized by its extreme protease resistance.

Purification and Characterization of Two Voltage-Dependent Anion Channel Isoforms from Plant Seeds

“…This could reflect the evolutionary diversity of vdac genes in monocotyledons and dicotyledons (Elkeles et al, 1995). The N-terminal sequence of VDAC proteins has the characteristics of an amphipathic ␣-helix and may be involved in targeting the cytoplasmatically synthesized proteins to the mitochondrial outer membrane (Kleene et al, 1987;Pfaller et al, 1990). Digestion of the two VDACs purified from bean seeds with the protease V8 led to specific peptide mapping, which indicates that sequence differences between the two isoforms are not restricted to the amino terminal domain but occur throughout the protein.…”

Biogenesis and transmembrane topology of the CHIP28 water channel at the endoplasmic reticulum.

“…However, for posttranslational membrane insertion, the reporter technique may produce erroneous results because secondary structure required for membrane insertion may require synthesis of residues downstream from the reporter fusion site. Posttranslational membrane insertion has been observed for certain proteins with extensive/3 sheet structure, such as porins, (Pfaller et al, 1990;Marmella, 1990;Mayer et al, 1993;Sugawara and Nikaido, 1992) and o~-helical proteins, such as annexins (Brisson et al, 1991;Lewit-Bently et al, 1992;Concha et al, 1993). Integration of the amino half of CHIP28 (residues 1-107), independent of the carboxy terminus, and identification of internal sequences within CHIP28, which direct biogenesis at the ER membrane, strongly support a cotranslational model of CHIP28 biogenesis, as has been previously shown for other polytopic eukaryotic proteins (BraeU and Lodish, 1982;Brown and Simoni, 1984;Wessels and Spiess, 1988;Audigier et al, 1987;.…”

Porin-type1 proteins in sarcoplasmic reticulum and plasmalemma of striated muscle fibres

“…Porin channels are synthesized in the cytoplasm and their incorporation into the mitochondrial OM is thought to require a receptor protein and nucleotide triphosphates (Pfaller et al, 1990). On the other hand, both plasmalemma and endoplasmic reticulum integral membrane proteins are synthesized on rough endoplasmic reticulum.…”