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Related Concept Videos

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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Single-pass Transmembrane Proteins01:25

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Integral membrane proteins are tightly associated with the cell membrane and play a crucial role in cell communication, signaling, adhesion, and transport of the molecules. Some integral membrane proteins are present only in the membrane monolayer. For example, the enzyme fatty acid amide hydrolase is present in the cytoplasmic side of the membrane monolayer. In contrast, another type of integral membrane protein, also known as a transmembrane protein, spans across the membrane. Transmembrane...
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Structure of Porins01:21

Structure of Porins

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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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Tight Junctions

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Tight junctions are molecular seals between cells that prevent the leaking of fluids, ions, and other small solutes across cavities and compartments in multicellular organisms. They are mainly composed of claudin and occludin transmembrane proteins, and other proteins such as tricellulin and JAM (junctional adhesion molecule). All these proteins are 4-pass transmembrane proteins, except JAM, which is a single-pass transmembrane protein belonging to the immunoglobulin superfamily. The...
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Porin Insertion in the Outer Mitochondrial Membrane01:12

Porin Insertion in the Outer Mitochondrial Membrane

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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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Aquaporins01:25

Aquaporins

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Aquaporins or AQPs are a family of integral membrane proteins whose primary function is to transport water, while some called aquaglyceroporins also transport glycerol. In addition, aquaporins have also been suspected to be involved in transporting volatile substances, such as carbon dioxide and ammonia, across membranes. Such AQPs that act as gas channels are often highly expressed in cells involved in the gaseous exchange, such as red blood cells, epithelial cells, and pulmonary capillaries.
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Membrane Transport Processes Analyzed by a Highly Parallel Nanopore Chip System at Single Protein Resolution
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Functional truncated membrane pores.

David Stoddart1, Mariam Ayub, Lajos Höfler

  • 1Department of Chemistry, University of Oxford, Oxford OX1 3TA, United Kingdom.

Proceedings of the National Academy of Sciences of the United States of America
|January 29, 2014
PubMed
Summary
This summary is machine-generated.

Researchers discovered a third class of membrane proteins that stabilize lipid pores, forming toroidal structures. These proteins, even when truncated, induce pore formation and ionic currents in cell membranes.

Keywords:
alpha-hemolysinbeta-barrellipid reorganizationnanopore

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Area of Science:

  • Biochemistry
  • Molecular Biology
  • Biophysics

Background:

  • Membrane proteins are crucial for cellular function, traditionally classified as integral or peripheral.
  • Integral proteins span the lipid bilayer, while peripheral proteins associate with the membrane surface.

Purpose of the Study:

  • To investigate a potential third class of membrane proteins.
  • To explore the mechanism of pore stabilization by truncated staphylococcal α-hemolysin mutants.
  • To understand the role of protein-stabilized lipid pores in biological processes.

Main Methods:

  • Utilizing truncated staphylococcal α-hemolysin mutants to create protein-lipid structures.
  • Measuring transmembrane ionic currents to detect pore formation.
  • Conducting molecular dynamics simulations to analyze pore stability.
  • Investigating lipid and voltage dependencies of pore formation.

Main Results:

  • Truncated staphylococcal α-hemolysin mutants induced well-defined transmembrane ionic currents.
  • These structures stabilized lipid pores, likely in toroidal configurations.
  • Pore formation was confirmed by lipid/voltage dependence and simulations.
  • Evidence supports a new class of membrane proteins stabilizing lipid pores.

Conclusions:

  • A novel class of membrane proteins stabilizes lipid pores, forming toroidal structures.
  • These stabilized lipid pores have implications for diseases like amyloidosis.
  • The findings are relevant to antimicrobial peptide action and immune system complexes.