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Primary structure of major outer membrane protein II (ompA protein) of Escherichia coli K-12
Abstract:
The amino acid sequence of major outer membrane protein II (ompA protein) from Escherichia coli K-12 has been determined. The transmembrane polypeptide consists of 325 residues, resulting in a molecular weight of 35,159. The transmembrane part of the protein is located between residues 1 and 177. In this part of the protein a predominantly lipophilic 27-residue segment exists that perhaps spans the membrane in a mostly alpha-helical conformation, or a 19-residue stretch of this segment might traverse the membrane linearly. Inside the outer membrane a sequence -Ala-Pro-Ala-Pro-Ala-Pro-Ala-Pro- exists that, analogous to the -Cys-Pro-Pro-Cys-Pro- sequence in the hinge region of immunoglobulin, could assume the conformation of a polyproline helix. Computer analysis did not reveal a clear overall pattern of internal homology in the protein; besides the -Ala-Pro- repeat, only one local area (two adjacent dodecapeptide segments) shows some repetitiveness. The same analysis did not produce evidence for internal homology in the previously determined sequence of outer membrane protein I (porin) nor was any marked resemblance detected between transmembrane proteins I and II.
Insights
The amino acid sequence of Escherichia coli K-12 outer membrane protein II (ompA protein) was determined. This transmembrane protein features a lipophilic segment potentially forming an alpha-helix or linear structure within the membrane.
Area of Science:
- Biochemistry
- Molecular Biology
- Microbiology
Background:
- Outer membrane proteins are crucial components of Gram-negative bacteria.
- Understanding protein structure aids in comprehending bacterial cell envelope function.
Purpose of the Study:
- To determine the complete amino acid sequence of major outer membrane protein II (ompA protein) from Escherichia coli K-12.
- To analyze the structural features and potential membrane-spanning regions of ompA protein.
Main Methods:
- Amino acid sequencing of ompA protein.
- Computer-aided analysis of protein sequence for homology and structural motifs.
Main Results:
- The ompA protein sequence comprises 325 residues with a molecular weight of 35,159.
- A lipophilic segment (residues 1-177) is identified as the transmembrane region, possibly adopting alpha-helical or linear conformations.
- A repeating Ala-Pro sequence suggests a polyproline helix structure.
Conclusions:
- The determined sequence provides a foundation for understanding ompA protein's structure-function relationship.
- No significant internal homology was found, nor resemblance to outer membrane protein I (porin).