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Bacterial outer membrane porins have a robust beta-barrel structure and therefore show potential for use as stochastic sensors based on single-molecule detection. The monomeric porin OmpG is especially attractive compared with multisubunit proteins because appropriate modifications of the pore can be easily achieved by mutagenesis. However, the gating of OmpG causes transient current blockades in single-channel recordings that would interfere with analyte detection. To eliminate this spontaneous gating activity, we used molecular dynamics simulations to identify regions of OmpG implicated in the gating. Based on our findings, two approaches were used to enhance the stability of the open conformation by site-directed mutagenesis. First, the mobility of loop 6 was reduced by introducing a disulfide bond between the extracellular ends of strands beta12 and beta13. Second, the interstrand hydrogen bonding between strands beta11 and beta12 was optimized by deletion of residue D215. The OmpG porin with both stabilizing mutations exhibited a 95% reduction in gating activity. We used this mutant for the detection of adenosine diphosphate at the single-molecule level, after equipping the porin with a cyclodextrin molecular adapter, thereby demonstrating its potential for use in stochastic sensing applications.

Original publication

DOI

10.1073/pnas.0711561105

Type

Journal article

Journal

Proc Natl Acad Sci U S A

Publication Date

29/04/2008

Volume

105

Pages

6272 - 6277

Keywords

Adenosine Diphosphate, Bacterial Outer Membrane Proteins, Biosensing Techniques, Computer Simulation, Escherichia coli Proteins, Hydrogen Bonding, Ion Channel Gating, Models, Molecular, Mutant Proteins, Porins, Principal Component Analysis, Protein Conformation, Protein Engineering, Stochastic Processes, beta-Cyclodextrins