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Single-pass Transmembrane Proteins

Single-pass Transmembrane Proteins

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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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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Insertion of Multi-pass Transmembrane Proteins in the RER

Insertion of Multi-pass Transmembrane Proteins in the RER

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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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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.
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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 precursors...

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Related Experiment Video

Updated: Jul 8, 2026

Monitoring the Assembly of a Secreted Bacterial Virulence Factor Using Site-specific Crosslinking

Monitoring the Assembly of a Secreted Bacterial Virulence Factor Using Site-specific Crosslinking

Published on: December 17, 2013

Structural and functional roles of the surface-exposed loops of the beta-barrel membrane protein OmpA from

¹Max-Planck-Institut für Biologie, Abteilung Mikrobiologie, D-72076 Tübingen, Germany. koebnik@iname.com

Journal of Bacteriology

|June 15, 1999

Summary

Surface-exposed loops on the OmpA protein are not essential for outer membrane assembly or stability. However, these loops are crucial for bacteriophage K3 binding and bacterial conjugation.

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Last Updated: Jul 8, 2026

Monitoring the Assembly of a Secreted Bacterial Virulence Factor Using Site-specific Crosslinking

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Published on: December 17, 2013

From Constructs to Crystals – Towards Structure Determination of β-barrel Outer Membrane Proteins

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Directed Protein Packaging within Outer Membrane Vesicles from Escherichia coli: Design, Production and Purification

Directed Protein Packaging within Outer Membrane Vesicles from Escherichia coli: Design, Production and Purification

Published on: November 16, 2016

Area of Science:

Structural biology
Membrane protein biogenesis
Bacterial outer membrane proteins

Background:

The N-terminal domain of Escherichia coli OmpA protein is an integral membrane protein.
It forms an antiparallel beta-barrel structure crucial for studying membrane protein assembly.
Surface-exposed loops play roles in protein function and interactions.

Purpose of the Study:

To investigate the structural and functional significance of surface-exposed loops in the OmpA protein.
To determine the necessity of these loops for outer membrane assembly, stability, and specific functions.

Main Methods:

Systematic deletion of individual and combined surface-exposed loops of the OmpA protein.
Analysis of mutant protein assembly into the outer membrane and their topology.
Assessment of thermal stability, bacteriophage receptor function, and role in bacterial conjugation.

Main Results:

All loop deletion mutants assembled efficiently into the outer membrane with wild-type topology.
Loop shortening did not affect the thermal stability of the OmpA protein.
Most mutants lost bacteriophage K3 receptor function and the ability to stabilize mating aggregates during F conjugation, except for the fourth loop deletion variant.

Conclusions:

Surface-exposed loops of OmpA are not required for its membrane insertion or stability.
These loops are essential for OmpA's function as a bacteriophage receptor and in stabilizing mating aggregates.
A minimal OmpA variant with all loops deleted represents the smallest known beta-structured integral membrane protein, aiding in artificial protein design.