PMID:10368142
| Citation |
Koebnik, R (1999) Structural and functional roles of the surface-exposed loops of the beta-barrel membrane protein OmpA from Escherichia coli. J. Bacteriol. 181:3688-94 |
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| Abstract |
The N-terminal domain of the OmpA protein from Escherichia coli, consisting of 170 amino acid residues, is embedded in the outer membrane, in the form of an antiparallel beta-barrel whose eight transmembrane beta-strands are connected by three short periplasmic turns and four relatively large surface-exposed hydrophilic loops. This protein domain serves as a paradigm for the study of membrane assembly of integral beta-structured membrane proteins. In order to dissect the structural and functional roles of the surface-exposed loops, they were shortened separately and in all possible combinations. All 16 loop deletion mutants assembled into the outer membrane with high efficiency and adopted the wild-type membrane topology. This systematic approach proves the absence of topogenic signals (e.g., in the form of loop sizes or charge distributions) in these loops. The shortening of surface-exposed loops did not reduce the thermal stability of the protein. However, none of the mutant proteins, with the exception of the variant with the fourth loop shortened, served as a receptor for the OmpA-specific bacteriophage K3. Furthermore, all loops were necessary for the OmpA protein to function in the stabilization of mating aggregates during F conjugation. An OmpA deletion variant with all four loops shortened, consisting of only 135 amino acid residues, constitutes the smallest beta-structured integral membrane protein known to date. These results represent a further step toward the development of artificial outer membrane proteins. |
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| Keywords |
Amino Acid Sequence; Bacterial Outer Membrane Proteins/chemistry; Bacterial Outer Membrane Proteins/genetics; Bacterial Outer Membrane Proteins/metabolism; Base Sequence; Cell Membrane/metabolism; Conjugation, Genetic; Escherichia coli/genetics; Escherichia coli/metabolism; Models, Molecular; Molecular Sequence Data; Mutagenesis, Insertional; Mutagenesis, Site-Directed; Protein Structure, Secondary; Recombinant Proteins/chemistry; Recombinant Proteins/metabolism; Sequence Deletion |
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