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Biogenesis of beta-barrel membrane proteins in bacteria and eukaryotes: evolutionary conservation and divergence.

Walther DM, Rapaport D, Tommassen J - Cell. Mol. Life Sci. (2009)

Bottom Line: This situation is thought to reflect the evolutionary origin of mitochondria and chloroplasts from Gram-negative bacterial endosymbionts. beta-barrel proteins fulfil a variety of functions; among them are pore-forming proteins that allow the flux of metabolites across the membrane by passive diffusion, active transporters of siderophores, enzymes, structural proteins, and proteins that mediate protein translocation across or insertion into membranes.The biogenesis process of these proteins combines evolutionary conservation of the central elements with some noticeable differences in signals and machineries.This review summarizes our current knowledge of the functions and biogenesis of this special family of proteins.

View Article: PubMed Central - PubMed

Affiliation: Interfaculty Institute for Biochemistry, University of Tübingen, Hoppe-Seyler-Str. 4, 72076, Tübingen, Germany.

ABSTRACT
Membrane-embedded beta-barrel proteins span the membrane via multiple amphipathic beta-strands arranged in a cylindrical shape. These proteins are found in the outer membranes of Gram-negative bacteria, mitochondria and chloroplasts. This situation is thought to reflect the evolutionary origin of mitochondria and chloroplasts from Gram-negative bacterial endosymbionts. beta-barrel proteins fulfil a variety of functions; among them are pore-forming proteins that allow the flux of metabolites across the membrane by passive diffusion, active transporters of siderophores, enzymes, structural proteins, and proteins that mediate protein translocation across or insertion into membranes. The biogenesis process of these proteins combines evolutionary conservation of the central elements with some noticeable differences in signals and machineries. This review summarizes our current knowledge of the functions and biogenesis of this special family of proteins.

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Working model for the biogenesis of mitochondrial β-barrel proteins. Precursors are synthesized in the cytosol and are probably guided to the mitochondrial surface by chaperones (1). At the mitochondrial surface, precursors are engaged by the primary import receptors of the TOM complex, predominantly via an interaction with Tom20. Subsequently, they are translocated through the TOM pore across the mitochondrial outer membrane (OM) into the intermembrane space (IMS) (2), where they interact with the small Tim protein complexes, which exert a chaperone-like function (3). Through a second step of recognition, the precursor proteins are sorted to the TOB complex, which then promotes their integration into the lipid core of the outer membrane (4)
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Fig3: Working model for the biogenesis of mitochondrial β-barrel proteins. Precursors are synthesized in the cytosol and are probably guided to the mitochondrial surface by chaperones (1). At the mitochondrial surface, precursors are engaged by the primary import receptors of the TOM complex, predominantly via an interaction with Tom20. Subsequently, they are translocated through the TOM pore across the mitochondrial outer membrane (OM) into the intermembrane space (IMS) (2), where they interact with the small Tim protein complexes, which exert a chaperone-like function (3). Through a second step of recognition, the precursor proteins are sorted to the TOB complex, which then promotes their integration into the lipid core of the outer membrane (4)

Mentions: Newly synthesized mitochondrial β-barrel proteins are initially recognized by the receptor components of the TOM complex, Tom20 and Tom70. They are then translocated through the import pore of the TOM complex and relayed to the TOB/SAM complex, which mediates their insertion into the OM. On their way from the TOM to the TOB complex, the precursor proteins are exposed to the IMS where they interact with small Tim components (Fig. 3). A major part of our knowledge about the biogenesis of β-barrel proteins results from studies on Tom40, the key component of the TOM complex. A major advantage for studying the protein’s assembly lies in the fact that several distinct assembly intermediates can be followed over time when radiolabeled Tom40 precursors are imported into isolated mitochondria and subsequently analyzed by Blue Native PAGE (reviewed in [60, 61]). In the following sections, steps in the biogenesis of β-barrel proteins and the components involved will be discussed.Fig. 3


Biogenesis of beta-barrel membrane proteins in bacteria and eukaryotes: evolutionary conservation and divergence.

Walther DM, Rapaport D, Tommassen J - Cell. Mol. Life Sci. (2009)

Working model for the biogenesis of mitochondrial β-barrel proteins. Precursors are synthesized in the cytosol and are probably guided to the mitochondrial surface by chaperones (1). At the mitochondrial surface, precursors are engaged by the primary import receptors of the TOM complex, predominantly via an interaction with Tom20. Subsequently, they are translocated through the TOM pore across the mitochondrial outer membrane (OM) into the intermembrane space (IMS) (2), where they interact with the small Tim protein complexes, which exert a chaperone-like function (3). Through a second step of recognition, the precursor proteins are sorted to the TOB complex, which then promotes their integration into the lipid core of the outer membrane (4)
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2724633&req=5

Fig3: Working model for the biogenesis of mitochondrial β-barrel proteins. Precursors are synthesized in the cytosol and are probably guided to the mitochondrial surface by chaperones (1). At the mitochondrial surface, precursors are engaged by the primary import receptors of the TOM complex, predominantly via an interaction with Tom20. Subsequently, they are translocated through the TOM pore across the mitochondrial outer membrane (OM) into the intermembrane space (IMS) (2), where they interact with the small Tim protein complexes, which exert a chaperone-like function (3). Through a second step of recognition, the precursor proteins are sorted to the TOB complex, which then promotes their integration into the lipid core of the outer membrane (4)
Mentions: Newly synthesized mitochondrial β-barrel proteins are initially recognized by the receptor components of the TOM complex, Tom20 and Tom70. They are then translocated through the import pore of the TOM complex and relayed to the TOB/SAM complex, which mediates their insertion into the OM. On their way from the TOM to the TOB complex, the precursor proteins are exposed to the IMS where they interact with small Tim components (Fig. 3). A major part of our knowledge about the biogenesis of β-barrel proteins results from studies on Tom40, the key component of the TOM complex. A major advantage for studying the protein’s assembly lies in the fact that several distinct assembly intermediates can be followed over time when radiolabeled Tom40 precursors are imported into isolated mitochondria and subsequently analyzed by Blue Native PAGE (reviewed in [60, 61]). In the following sections, steps in the biogenesis of β-barrel proteins and the components involved will be discussed.Fig. 3

Bottom Line: This situation is thought to reflect the evolutionary origin of mitochondria and chloroplasts from Gram-negative bacterial endosymbionts. beta-barrel proteins fulfil a variety of functions; among them are pore-forming proteins that allow the flux of metabolites across the membrane by passive diffusion, active transporters of siderophores, enzymes, structural proteins, and proteins that mediate protein translocation across or insertion into membranes.The biogenesis process of these proteins combines evolutionary conservation of the central elements with some noticeable differences in signals and machineries.This review summarizes our current knowledge of the functions and biogenesis of this special family of proteins.

View Article: PubMed Central - PubMed

Affiliation: Interfaculty Institute for Biochemistry, University of Tübingen, Hoppe-Seyler-Str. 4, 72076, Tübingen, Germany.

ABSTRACT
Membrane-embedded beta-barrel proteins span the membrane via multiple amphipathic beta-strands arranged in a cylindrical shape. These proteins are found in the outer membranes of Gram-negative bacteria, mitochondria and chloroplasts. This situation is thought to reflect the evolutionary origin of mitochondria and chloroplasts from Gram-negative bacterial endosymbionts. beta-barrel proteins fulfil a variety of functions; among them are pore-forming proteins that allow the flux of metabolites across the membrane by passive diffusion, active transporters of siderophores, enzymes, structural proteins, and proteins that mediate protein translocation across or insertion into membranes. The biogenesis process of these proteins combines evolutionary conservation of the central elements with some noticeable differences in signals and machineries. This review summarizes our current knowledge of the functions and biogenesis of this special family of proteins.

Show MeSH