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Multi-pass Transmembrane Proteins and β-barrels01:09

Multi-pass Transmembrane Proteins and β-barrels

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In multi-pass transmembrane proteins, the polypeptide chain crosses the membrane more than once. The transmembrane polypeptide chain either forms an α-helix or β-strand structure. α-Helix containing multi-pass transmembrane proteins are ubiquitous, whereas β-strand containing ones are mainly found in gram-negative bacteria, mitochondria, and chloroplasts.
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Structure of Porins01:21

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Mitochondria, chloroplasts, and gram-negative bacteria have transmembrane, beta-barrel proteins called porins to mediate the free diffusion of ions and metabolites across the membrane. Mitochondrial porin precursors contain conserved amino acid sequences called beta signals at their C-terminal. Beta signals have a  motif of PoXGXXHyXHy (Po-Polar, X-Any amino acid, G-Glycine, Hy-LargeHydrophobic), which are crucial for precursor recognition to initiate precursor assembly. Beta-barrel...
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Porin Insertion in the Outer Mitochondrial Membrane01:12

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Porins are beta-barrel proteins translocated to the mitochondrial outer membrane through the TOM complex into the intermembrane space. Porin precursors bind TIM chaperones within the intermembrane space and are guided to the Sorting and Assembly Machinery complex or SAM complex on the outer mitochondrial membrane.
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Protein Folding01:25

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Proteins are chains of amino acids linked together by peptide bonds. Upon synthesis, a protein folds into a three-dimensional conformation, critical to its biological function. Interactions between its constituent amino acids guide protein folding, and hence the protein structure is primarily dependent on its amino acid sequence.
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Mitochondrial protein import is powered by two distinct energy sources: ATP hydrolysis and electrochemical potential across the inner membrane. Newly synthesized precursors are bound by cytosolic chaperones of the Hsp70 family, which guide them to the import receptors on the mitochondrial surface. Utilizing the energy of ATP hydrolysis, Hsp70 chaperones transfer these precursors to the TOM receptors on the mitochondrial outer membrane.
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From Constructs to Crystals &#8211; Towards Structure Determination of &#946;-barrel Outer Membrane Proteins
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Transmembrane β-barrels: Evolution, folding and energetics.

Deepti Chaturvedi1, Radhakrishnan Mahalakshmi1

  • 1Molecular Biophysics Laboratory, Department of Biological Sciences, Indian Institute of Science Education and Research, Bhopal 462066, India.

Biochimica Et Biophysica Acta. Biomembranes
|September 26, 2017
PubMed
Summary
This summary is machine-generated.

The biogenesis of transmembrane β-barrels (outer membrane proteins, or OMPs) involves complex protein folding machinery. This study explores OMP evolution, folding mechanisms, and stability, highlighting key questions in their biogenesis and proteostasis.

Keywords:
Assisted foldingBarrel assembly machineryBiogenesisEnergeticsKinetic controlMitochondrial outer membrane proteinsOMP

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Area of Science:

  • Biochemistry
  • Molecular Biology
  • Evolutionary Biology

Background:

  • Transmembrane β-barrels (outer membrane proteins, or OMPs) are crucial for cellular function.
  • OMP biogenesis involves intricate interactions with translocases, assembly machinery, and chaperones.
  • Existing theories explain in vivo chaperone-assisted and in vitro spontaneous folding mechanisms.

Purpose of the Study:

  • To review and deliberate known aspects of β-barrel evolution, folding, and stability.
  • To highlight outstanding questions in the field of β-barrel biogenesis and proteostasis.
  • To compare structural and mechanistic similarities/differences between prokaryotic and eukaryotic β-barrels.

Main Methods:

  • Literature review and synthesis of existing research on OMP biogenesis.
  • Comparative analysis of structural features (strand numbers) in bacterial and mitochondrial β-barrels.
  • Discussion of evolutionary links and folding mechanisms.

Main Results:

  • Bacterial OMPs have even-numbered strands; mitochondrial β-barrels can be even- or odd-stranded.
  • Similarities exist between prokaryotic and eukaryotic β-barrel folding machinery, but evolutionary origins remain unclear.
  • OMPs share conserved biophysical attributes and structures despite sequence and functional diversity.

Conclusions:

  • Understanding OMP assembly is vital, especially for complex eukaryotic β-barrels.
  • Further research is needed to clarify the evolutionary origins and precise biogenesis pathways of β-barrels.
  • Key questions remain regarding OMP stability and proteostasis regulation across different organisms.