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Membrane assembly of circularly permuted variants of the E. coli outer membrane protein OmpA
Abstract:
The two-domain, 325 residue outer membrane protein OmpA is one of the most abundant proteins of Escherichia coli, playing a role in the maintenance of the integrity of the cell surface. The N-terminal domain, consisting of about 170 amino acid residues, is embedded in the membrane, presumably in the form of a beta-barrel consisting of eight amphipathic transmembrane strands. Pairs of these proposed transmembrane strands were permuted at the DNA level, in order to dissect the process of membrane assembly. All three possible circular permutations led to variants, which were, in comparison with the wild-type protein, less efficiently assembled. In contrast, no membrane assembly could be detected in any of 18 non-circularly permuted variants. We take this as an indication that the "right" (wild-type) order of beta-strands is a necessary and sufficient prerequisite for at least partially successful membrane assembly. This may be the consequence of packing constraints and/or a failure to adopt the wild-type arrangement of beta-strands, which require crossing of the periplasmic turns.
Insights
The outer membrane protein A (OmpA) requires a specific beta-strand order for Escherichia coli cell surface integrity. Permuting these strands hinders or prevents proper membrane assembly.
Area of Science:
- Microbiology
- Structural Biology
- Biochemistry
Background:
- Outer membrane protein A (OmpA) is abundant in Escherichia coli, crucial for cell surface integrity.
- OmpA features an N-terminal domain embedded in the membrane as a beta-barrel of eight transmembrane strands.
Purpose of the Study:
- To investigate the role of beta-strand order in OmpA membrane assembly.
- To determine if the wild-type arrangement of beta-strands is essential for OmpA function.
Main Methods:
- DNA-level permutation of transmembrane beta-strands within the OmpA gene.
- Analysis of membrane assembly efficiency for wild-type and variant OmpA proteins.
Main Results:
- Circular permutations of OmpA beta-strands resulted in less efficient membrane assembly compared to wild-type.
- Non-circularly permuted variants showed no detectable membrane assembly.
- The wild-type order of beta-strands appears necessary for successful OmpA membrane integration.
Conclusions:
- The specific sequence and arrangement of beta-strands are critical for OmpA's proper membrane assembly.
- Deviations from the wild-type strand order may lead to assembly failure due to packing constraints or improper folding.