Biogenesis of mitochondrial β-barrel proteins: the POTRA domain is involved in precursor release from the SAM complex.

The mitochondrial outer membrane contains proteinaceous machineries for the translocation of precursor proteins. The sorting and assembly machinery (SAM) is required for the insertion of β-barrel proteins into the outer membrane. Sam50 is the channel-forming core subunit of the SAM complex and belongs to the BamA/Sam50/Toc75 family of proteins that have been conserved from Gram-negative bacteria to mitochondria and chloroplasts.

Biogenesis of the mitochondrial TOM complex: Mim1 promotes insertion and assembly of signal-anchored receptors.

The translocase of the outer membrane (TOM complex) is the central entry gate for nuclear-encoded mitochondrial precursor proteins. All Tom proteins are also encoded by nuclear genes and synthesized as precursors in the cytosol. The channel-forming beta-barrel protein Tom40 is targeted to mitochondria via Tom receptors and inserted into the outer membrane by the sorting and assembly machinery (SAM complex).

The morphology proteins Mdm12/Mmm1 function in the major beta-barrel assembly pathway of mitochondria.

The beta-barrel proteins of mitochondria are synthesized on cytosolic ribosomes. The proteins are imported by the translocase of the outer membrane (TOM) and the sorting and assembly machinery (SAM). It has been assumed that the SAM(core) complex with the subunits Sam35, Sam37 and Sam50 represents the last import stage common to all beta-barrel proteins, followed by splitting in a Tom40-specific route and a route for other beta-barrel proteins.

The essential mitochondrial protein Erv1 cooperates with Mia40 in biogenesis of intermembrane space proteins.

The proteins of the mitochondrial intermembrane space (IMS) are encoded by nuclear genes and synthesized on cytosolic ribosomes. While some IMS proteins are imported by the classical presequence pathway that involves the membrane potential deltapsi across the inner mitochondrial membrane and proteolytic processing to release the mature protein to the IMS, the import of numerous small IMS proteins is independent of a deltapsi and does not include proteolytic processing. The biogenesis of small IMS proteins requires an essential mitochondrial IMS import and assembly protein, termed Mia40.

Essential role of Mia40 in import and assembly of mitochondrial intermembrane space proteins.

Mitochondria import nuclear-encoded precursor proteins to four different subcompartments. Specific import machineries have been identified that direct the precursor proteins to the mitochondrial outer membrane, inner membrane or matrix, respectively. However, a machinery dedicated to the import of mitochondrial intermembrane space (IMS) proteins has not been found so far.

Biogenesis of the protein import channel Tom40 of the mitochondrial outer membrane: intermembrane space components are involved in an early stage of the assembly pathway.

Tom40 forms the central channel of the preprotein translocase of the mitochondrial outer membrane (TOM complex). The precursor of Tom40 is encoded in the nucleus, synthesized in the cytosol, and imported into mitochondria via a multi-step assembly pathway that involves the mature TOM complex and the sorting and assembly machinery of the outer membrane (SAM complex). We report that opening of the mitochondrial intermembrane space by swelling blocks the assembly pathway of the beta-barrel protein Tom40.

Influence of redox-active compounds and PXR-activators on human MRP1 and MRP2 gene expression.

In the present study, we investigated the inducibility of the drug conjugate transporter genes MRP1 and MRP2 by redox-active compounds such as tertiary butylated hydroquinone (tBHQ) and quercetin and by chemicals known to activate the pregnane X receptor (PXR) such as rifampicin and clotrimazol and by the metalloid compound arsenite. The human MRP2 gene was found to be inducible in HepG2 cells by rifampicin, clotrimazol, arsenite and tBHQ. As MRP1 expression is extremely low in HepG2 cells, its inducibility was studied in MCF-7 cells.