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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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Crystal structure of a bacterial β-barrel outer membrane protein. Left: a ribbon representation of the structure of LpxR, a lipid A deacylase of Salmonella typhimurium [133]. The 12-stranded β-barrel consists of all anti-parallel β-strands, which are connected by short turns at the periplasmic side (bottom) and longer loops including some α-helical segments at the extracellular side (top). The ribbon is colored with a gradient from the N terminus in blue to the C terminus in red. Right a top view of the protein (the figure was kindly provided by Lucy Rutten)
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Fig1: Crystal structure of a bacterial β-barrel outer membrane protein. Left: a ribbon representation of the structure of LpxR, a lipid A deacylase of Salmonella typhimurium [133]. The 12-stranded β-barrel consists of all anti-parallel β-strands, which are connected by short turns at the periplasmic side (bottom) and longer loops including some α-helical segments at the extracellular side (top). The ribbon is colored with a gradient from the N terminus in blue to the C terminus in red. Right a top view of the protein (the figure was kindly provided by Lucy Rutten)

Mentions: Gram-negative bacteria are enveloped by two membranes, the inner and the outer. The space between these membranes, the periplasm, contains the cell wall, which consists of peptidoglycan. While the inner membrane is a regular phospholipid bilayer, the outer membrane (OM) is an asymmetrical bilayer consisting of phospholipids and lipopolysaccharides (LPS) in the inner and outer leaflets, respectively. Furthermore, the integral membrane proteins of the inner and outer membrane are structurally different. While integral inner membrane proteins typically span the membrane in the form of hydrophobic α-helices, most integral outer membrane proteins (OMPs) are β-barrels consisting of antiparallel amphipathic β-strands [1] (see Fig. 1 for an example of the structure of a membrane-embedded β-barrel protein). A notable exception is Wza, the OM transporter for capsular polysaccharides. Each protomer of this octameric protein contributes an amphipathic α-helix to a barrel of α-helices that is embedded in the membrane [2]. The general absence of hydrophobic α-helices in OMPs is probably related to the fact that they have to be transported across the inner membrane to reach their destination; they would be retained in the inner membrane if they contained hydrophobic α-helices (see below). Apart from integral membrane proteins, the OM also contains lipoproteins, which are attached to the membrane via an N-terminal N-acyl-diacylglycerylcysteine moiety. For the biogenesis of these lipoproteins, which will not be discussed here, the reader is referred to other reviews [3, 4].Fig. 1


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)

Crystal structure of a bacterial β-barrel outer membrane protein. Left: a ribbon representation of the structure of LpxR, a lipid A deacylase of Salmonella typhimurium [133]. The 12-stranded β-barrel consists of all anti-parallel β-strands, which are connected by short turns at the periplasmic side (bottom) and longer loops including some α-helical segments at the extracellular side (top). The ribbon is colored with a gradient from the N terminus in blue to the C terminus in red. Right a top view of the protein (the figure was kindly provided by Lucy Rutten)
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Related In: Results  -  Collection

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

Fig1: Crystal structure of a bacterial β-barrel outer membrane protein. Left: a ribbon representation of the structure of LpxR, a lipid A deacylase of Salmonella typhimurium [133]. The 12-stranded β-barrel consists of all anti-parallel β-strands, which are connected by short turns at the periplasmic side (bottom) and longer loops including some α-helical segments at the extracellular side (top). The ribbon is colored with a gradient from the N terminus in blue to the C terminus in red. Right a top view of the protein (the figure was kindly provided by Lucy Rutten)
Mentions: Gram-negative bacteria are enveloped by two membranes, the inner and the outer. The space between these membranes, the periplasm, contains the cell wall, which consists of peptidoglycan. While the inner membrane is a regular phospholipid bilayer, the outer membrane (OM) is an asymmetrical bilayer consisting of phospholipids and lipopolysaccharides (LPS) in the inner and outer leaflets, respectively. Furthermore, the integral membrane proteins of the inner and outer membrane are structurally different. While integral inner membrane proteins typically span the membrane in the form of hydrophobic α-helices, most integral outer membrane proteins (OMPs) are β-barrels consisting of antiparallel amphipathic β-strands [1] (see Fig. 1 for an example of the structure of a membrane-embedded β-barrel protein). A notable exception is Wza, the OM transporter for capsular polysaccharides. Each protomer of this octameric protein contributes an amphipathic α-helix to a barrel of α-helices that is embedded in the membrane [2]. The general absence of hydrophobic α-helices in OMPs is probably related to the fact that they have to be transported across the inner membrane to reach their destination; they would be retained in the inner membrane if they contained hydrophobic α-helices (see below). Apart from integral membrane proteins, the OM also contains lipoproteins, which are attached to the membrane via an N-terminal N-acyl-diacylglycerylcysteine moiety. For the biogenesis of these lipoproteins, which will not be discussed here, the reader is referred to other reviews [3, 4].Fig. 1

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