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  • Title: Gene duplication of the eight-stranded beta-barrel OmpX produces a functional pore: a scenario for the evolution of transmembrane beta-barrels.
    Author: Arnold T, Poynor M, Nussberger S, Lupas AN, Linke D.
    Journal: J Mol Biol; 2007 Mar 02; 366(4):1174-84. PubMed ID: 17217961.
    Abstract:
    The repeating unit of outer membrane beta-barrels from Gram-negative bacteria is the beta-hairpin, and representatives of this protein family always have an even strand number between eight and 22. Two dominant structural forms have eight and 16 strands, respectively, suggesting gene duplication as a possible mechanism for their evolution. We duplicated the sequence of OmpX, an eight-stranded beta-barrel protein of known structure, and obtained a beta-barrel, designated Omp2X, which can fold in vitro and in vivo. Using single-channel conductance measurements and PEG exclusion assays, we found that Omp2X has a pore size similar to that of OmpC, a natural 16-stranded barrel. Fusions of the homologous proteins OmpX, OmpA and OmpW were able to fold in vitro in all combinations tested, revealing that the general propensity to form a beta-barrel is sufficient to evolve larger barrels by simple genetic events.
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