Gene duplication of the eight-stranded beta-barrel OmpX produces a functional pore: a scenario for the evolution of transmembrane beta-barrels.
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.
Arnold
Thomas
T
Max Planck Institute for Developmental Biology, Department Protein Evolution, Spemannstr. 35, 72076 Tübingen, Germany.
Poynor
Melissa
M
Nussberger
Stephan
S
Lupas
Andrei N
AN
Linke
Dirk
D
D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D019143:Evolution, Molecular; D020440:Gene Duplication; D006867:Hydrolases / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D017510:Protein Folding; D017433:Protein Structure, Secondary
D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; C482905:OmpX protein, E coli; D006867:Hydrolases