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Stochastic sensing of organic analytes by a pore-forming protein containing a molecular adapter

Nature volume 398, pages 686–690 (1999)Cite this article

Abstract

The detection of organic molecules is important in many areas, including medicine, environmental monitoring and defence1,5. Stochastic sensing is an approach that relies on the observation of individual binding events between analyte molecules and a single receptor6. Engineered transmembrane protein pores are promising sensor elements for stochastic detection6, and in their simplest manifestation they produce a fluctuating binary (‘on/off’) response in the transmembrane electrical current. The frequency of occurrence of the fluctuations reveals the concentration of the analyte, and its identity can be deduced from the characteristic magnitude and/or duration of the fluctuations. Genetically engineered versions of the bacterial pore-forming protein α-haemolysin have been used to identify and quantify divalent metal ions in solution6. But it is not immediately obvious how versatile binding sites for organic ligands might be obtained by engineering of the pore structure. Here we show that stochastic sensing of organic molecules can be procured from α-haemolysin by equipping the channel with an internal, non-covalently bound molecular ‘adapter’ which mediates channel blocking by the analyte. We use cyclodextrins as the adapters because these fit comfortably inside the pore and present a hydrophobic cavity suitable for binding a variety of organic analytes. Moreover, a single sensing element of this sort can be used to analyse a mixture of organic molecules with different binding characteristics. We envisage the use of other adapters, so that the pore could be ‘programmed’ for a range of sensing functions.

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Figure 1: Bilayer recordings showing the interaction of a single α-haemolysin (αHL) pore with β-cyclodextrin (βCD) and.
Figure 2: Molecular graphics representation of the interaction between αHL and βCD.
Figure 3: A kinetic scheme for the interactions between α-haemolysin (αHL), β-cyclodextrin (βCD) and guests.
Figure 4: Response of αHL·βCD at different analyte concentrations.
Figure 5: Analysis of drug molecules by stochastic sensing with αHL and a βCD or γCD adapter.

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Acknowledgements

This work was supported by DARPA, DOE and ONR. We thank E. Gouaux for comments on the manuscript.

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Authors and Affiliations

  1. Department of Medical Biochemistry & Genetics, Texas A&M University Health Science Center, 440 Reynolds Medical Building, College Station, Texas, 77843-1114, USA

    Li-Qun Gu, Orit Braha, Sean Conlan & Stephen Cheley

  2. Department of Chemistry, Texas A&M University, College Station, Texas, 77843-255, USA

    Hagan Bayley

Authors
  1. Li-Qun Gu
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  2. Orit Braha
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  5. Hagan Bayley
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Correspondence to Orit Braha or Hagan Bayley.

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Gu, LQ., Braha, O., Conlan, S. et al. Stochastic sensing of organic analytes by a pore-forming protein containing a molecular adapter. Nature 398, 686–690 (1999). https://doi.org/10.1038/19491

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