Evolutionary conservation of biogenesis of β-barrel membrane proteins
ABSTRACT The outer membranes of mitochondria and chloroplasts are distinguished by the presence of beta-barrel membrane proteins. The outer membrane of Gram-negative bacteria also harbours beta-barrel proteins. In mitochondria these proteins fulfil a variety of functions such as transport of small molecules (porin/VDAC), translocation of proteins (Tom40) and regulation of mitochondrial morphology (Mdm10). These proteins are encoded by the nucleus, synthesized in the cytosol, targeted to mitochondria as chaperone-bound species, recognized by the translocase of the outer membrane, and then inserted into the outer membrane where they assemble into functional oligomers. Whereas some knowledge has been accumulated on the pathways of insertion of proteins that span cellular membranes with alpha-helical segments, very little is known about how beta-barrel proteins are integrated into lipid bilayers and assembled into oligomeric structures. Here we describe a protein complex that is essential for the topogenesis of mitochondrial outer membrane beta-barrel proteins (TOB). We present evidence that important elements of the topogenesis of beta-barrel membrane proteins have been conserved during the evolution of mitochondria from endosymbiotic bacterial ancestors.
- SourceAvailable from: Jérémy Guérin
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- "The superfamily also includes transporters in membranes of various organelles of endosymbiotic origin. Thus, Sam50/Tob55 is the central piece of a complex that mediates protein insertion into the outer membrane of mitochondria, and it is likely that Toc75-V (Oep80) has a similar function in chloroplasts (Hsu and Inoue, 2009; Paschen et al., 2003; Patel et al., 2008; Schleiff and Soll, 2005). Toc75-III is the core of a hetero-oligomeric complex involved in translocating proteins from the cytosol across the outer membrane of chloroplasts (Schleiff et al., 2003; Sommer et al., 2011). "
ABSTRACT: The two-partner secretion (TPS) pathway is a branch of type V secretion. TPS systems are dedicated to the secretion across the outer membrane of long proteins that form extended β-helices. They are composed of a 'TpsA' cargo protein and a 'TpsB' transporter, which belongs to the Omp85 superfamily. This basic design can be supplemented by additional components in some TPS systems. X-ray structures are available for the conserved TPS domain of several TpsA proteins and for one TpsB transporter. However, the molecular mechanisms of two-partner secretion remain to be deciphered, and in particular, the specific role(s) of the TPS domain and the conformational dynamics of the TpsB transporter. Deciphering the TPS pathway may reveal functional features of other transporters of the Omp85 superfamily.Research in Microbiology 03/2013; DOI:10.1016/j.resmic.2013.03.009 · 2.83 Impact Factor
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- "To study whether MINOS was involved in outer membrane protein biogenesis, we used the radiolabeled precursor of Tom40 as a model substrate. For this precursor, three assembly stages can be resolved by blue native electrophoresis of digitonin-lysed mitochondria (Model et al., 2001; Paschen et al., 2003; Wiedemann et al., 2003; Ishikawa et al., 2004; Chan and Lithgow, 2008; Dukanovic et al., 2009). On incubation with isolated mitochondria, Tom40 forms intermediate I, which represents interaction of the precursor with the SAM complex (Model et al., 2001; Wiedemann et al., 2003; Becker et al., 2010). "
ABSTRACT: Mitochondria contain two membranes, the outer membrane and the inner membrane with folded cristae. The mitochondrial inner membrane organizing system (MINOS) is a large protein complex required for maintaining inner membrane architecture. MINOS interacts with both preprotein transport machineries of the outer membrane, the translocase of the outer membrane (TOM) and the sorting and assembly machinery (SAM). It is unknown, however, whether MINOS plays a role in the biogenesis of outer membrane proteins. We have dissected the interaction of MINOS with TOM and SAM and report that MINOS binds to both translocases independently. MINOS binds to the SAM complex via the conserved polypeptide transport-associated domain of Sam50. Mitochondria lacking mitofilin, the large core subunit of MINOS, are impaired in the biogenesis of β-barrel proteins of the outer membrane, whereas mutant mitochondria lacking any of the other five MINOS subunits import β-barrel proteins in a manner similar to wild-type mitochondria. We show that mitofilin is required at an early stage of β-barrel biogenesis that includes the initial translocation through the TOM complex. We conclude that MINOS interacts with TOM and SAM independently and that the core subunit mitofilin is involved in biogenesis of outer membrane β-barrel proteins.Molecular biology of the cell 08/2012; 23(20):3948-3956. DOI:10.1091/mbc.E12-04-0295 · 5.98 Impact Factor
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- "The assembly pathway of Tom40 involves several steps. On initial import of the precursor by the TOM complex to the intermembrane space side, intermembrane space chaperone complexes transfer Tom40 to the sorting and assembly machinery (SAM complex ) of the outer membrane (Model et al., 2001; Kozjak et al., 2003; Paschen et al., 2003; Wiedemann et al., 2003, 2004; Gentle et al., 2004; Hoppins and Nargang, 2004). The interaction of the Tom40 precursor with the SAM complex can be directly monitored by blue native electrophoresis after lysis of the mitochondria with the nonionic detergent digitonin (Ryan et al., 2001; Wittig et al., 2006; Stojanovski et al., 2007). "
ABSTRACT: The preprotein translocase of the outer mitochondrial membrane (TOM) functions as the main entry gate for the import of nuclear-encoded proteins into mitochondria. The major subunits of the TOM complex are the three receptors Tom20, Tom22, and Tom70 and the central channel-forming protein Tom40. Cytosolic kinases have been shown to regulate the biogenesis and activity of the Tom receptors. Casein kinase 2 stimulates the biogenesis of Tom22 and Tom20, whereas protein kinase A (PKA) impairs the receptor function of Tom70. Here we report that PKA exerts an inhibitory effect on the biogenesis of the β-barrel protein Tom40. Tom40 is synthesized as precursor on cytosolic ribosomes and subsequently imported into mitochondria. We show that PKA phosphorylates the precursor of Tom40. The phosphorylated Tom40 precursor is impaired in import into mitochondria, whereas the nonphosphorylated precursor is efficiently imported. We conclude that PKA plays a dual role in the regulation of the TOM complex. Phosphorylation by PKA not only impairs the receptor activity of Tom70, but it also inhibits the biogenesis of the channel protein Tom40.Molecular biology of the cell 03/2012; 23(9):1618-27. DOI:10.1091/mbc.E11-11-0933 · 5.98 Impact Factor