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Related Concept Videos

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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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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Multi-pass Transmembrane Proteins and β-barrels01:09

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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.
α-Helix containing multi-pass transmembrane proteins
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Protein Complex Assembly02:41

Protein Complex Assembly

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Proteins can form homomeric complexes with another unit of the same protein or heteromeric complexes with different types.  Most protein complexes self-assemble spontaneously via ordered pathways, while some proteins need assembly factors that guide their proper assembly. Despite the crowded intracellular environment, proteins usually interact with their correct partners and form functional complexes.
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Protein Complex Assembly

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Protein Translocation Machinery on the ER Membrane01:28

Protein Translocation Machinery on the ER Membrane

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The translocon complex situated on the ER membrane is the main gateway for the protein secretory pathway. It facilitates the transport of nascent peptides into the ER lumen and their insertion into the ER membrane.
Sec61 protein conducting channel
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Related Experiment Video

Updated: Nov 24, 2025

From Constructs to Crystals &#8211; Towards Structure Determination of &#946;-barrel Outer Membrane Proteins
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From Constructs to Crystals – Towards Structure Determination of β-barrel Outer Membrane Proteins

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Structures of the β-barrel assembly machine recognizing outer membrane protein substrates.

Le Xiao1,2, Long Han1,2, Bufan Li1,2

  • 1National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.

FASEB Journal : Official Publication of the Federation of American Societies for Experimental Biology
|December 28, 2020
PubMed
Summary

The bacterial β-barrel assembly machinery (BAM) complex

Keywords:
Cryo-EMX-ray crystallographyouter membrane protein biogenesisthe BAM-substrate complexβ-signal hypothesis

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Area of Science:

  • Structural biology
  • Molecular biology
  • Biochemistry

Background:

  • Beta-barrel outer membrane proteins (β-OMPs) are essential for Gram-negative bacteria.
  • The β-barrel assembly machinery (BAM) complex facilitates β-OMP assembly.
  • The precise mechanism of BAM-mediated assembly is not fully understood.

Purpose of the Study:

  • To elucidate the structural mechanisms of the BAM complex during β-OMP assembly.
  • To investigate the role of membrane environment and substrate interaction in BAM function.

Main Methods:

  • X-ray crystallography to determine BAM complex structures in detergents and nanodisks.
  • Structural analysis of BAM complex with bound β-OMP substrates.
  • Functional analysis of substrate interactions.

Main Results:

  • BAM complex structures reveal dynamic conformations modulated by membrane composition.
  • Structures show the first β-strand of BamA (β1BamA) interacting with the last β-strand of a β-OMP substrate.
  • This interaction supports the β-signal hypothesis for β-OMP biogenesis.

Conclusions:

  • The BAM complex is highly dynamic, with its conformation influenced by the surrounding membrane.
  • The β1BamA strand likely interacts with the terminal β-strand of incoming β-OMP substrates.
  • This provides mechanistic insight into the initiation of β-OMP assembly.