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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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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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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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The movement of ions like sodium, potassium, and calcium into and out of the cell is essential to maintain the electrochemical gradient in living cells. The ion channels—a class of membrane transport proteins—help maintain this ionic gradient for the smooth functioning of physiological activities such as maintaining cell size and volume, conducting nerve impulses, and gas and nutrient exchange.
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Ion channels are specialized proteins on the plasma membrane that allow charged ions to pass down their electrochemical gradient. Their main function is to maintain the membrane potential which is critical for cell viability. These channels are either gated or non-gated and can transport more than a thousand ions within milliseconds for the cellular event to occur.
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Related Experiment Video

Updated: Nov 6, 2025

From Constructs to Crystals &#8211; Towards Structure Determination of &#946;-barrel Outer Membrane Proteins
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Constructing ion channels from water-soluble α-helical barrels.

Alistair J Scott1,2, Ai Niitsu1,3, Huong T Kratochvil4

  • 1School of Chemistry, University of Bristol, Bristol, UK.

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|May 11, 2021
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Summary

Designing membrane-spanning peptide ion channels is difficult. This study developed novel alpha-helical barrels that form cation-selective channels, revealing two distinct structural states in lipid bilayers.

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Area of Science:

  • Biophysical chemistry
  • Structural biology
  • Membrane biophysics

Background:

  • Designing self-assembling peptides into functional membrane ion channels presents significant challenges.
  • Simultaneous control over inter-peptide hydrophobic interactions and peptide-lipid interface interactions is crucial.

Purpose of the Study:

  • To rationally design and characterize novel alpha-helical peptide barrels capable of forming functional ion channels in lipid bilayers.
  • To investigate the structural dynamics and conformational changes of designed peptides within a membrane environment.

Main Methods:

  • Rational de novo design of water-soluble alpha-helical barrels with polar interiors.
  • High-resolution X-ray crystallography for structural confirmation.
  • Single-channel electrical recordings and fluorescent imaging in lipid bilayers.
  • X-ray crystallography in lipidic cubic phase and computational analyses.

Main Results:

  • Successfully designed and structurally confirmed alpha-helical barrels with water-filled lumens.
  • Demonstrated formation of monodisperse, cation-selective ion channels with unitary conductance in membranes.
  • Identified an alternative, constricted channel state via X-ray crystallography in lipidic cubic phase.
  • Computational analyses provided insights into the properties of different peptide states.

Conclusions:

  • The designed peptides can self-assemble into functional cation-selective ion channels in lipid bilayers.
  • Peptides can adopt distinct conformational states within the membrane, impacting channel function.
  • This multi-step design and characterization approach advances the field of artificial ion channel engineering.