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1.D.74 The Stimulus-responsive Synthetic p-Octiphenyl Stave Pore (SSOP) Family

The sensation of taste is mediated by activation or deactivation of transmembrane pores (Chandrashekar et al. 2006). Artificial stimulus-responsive pores are appealing as sensor components because changes in their activity are readily detectable in many different ways. Litvinchuk et al. 2007 presented synthetic pores that, like our tongues, can sense flavours in food and make them visibly detectable. They have been explored with synthetic receptor arrays and electronic tongues (Toko 1998). The ligands bind and block the synthetic pores. Reactive amplification proved to be highly sensitive and adaptable to various analytes and pores. The system was tested on real food samples for detection of sucrose, lactose, lactate, acetate, citrate and glutamate to demonstrate the feasibility of these synthetic pores as universal sensors.

As stimulus-responsive pores, artificial beta-barrels that are made from synthetic rigid p-octiphenyl 'staves' and held together by antiparallel short beta-sheets are used (Litvinchuk et al. 2007). The peptide sequence of rigid-rod beta-barrel was chosen to produce a hydrophobic exterior and a cationic interior covered with lysine–histidine (KH) dyads. This design produceed large pores in the lipid bilayer that mediated the fluorogenic release of self-quenched 5(6)-carboxyfluorescein (CF) from vesicles, and thus the optical 'naked eye' detection of pore activity. The cationic pore interior binds various anionic guests, the response to this chemical stimulation being pore blockage. The difference in pore blockage efficiency of ATP and ADP was particularly attractive because it enabled the following of enzymatic hydrolysis of ATP to ADP by simple blockage experiments. As an illustrative sensing application, Litvinchuk et al. 2007 determined the concentration of sucrose in a variety of soft drinks such as Coca-Cola or Red Bull by following the consumption of ATP during the degradation of sucrose by invertase and hexokinase as uncoupled signal generators (Litvinchuk et al. 2005).  Matile et al. 2011 have reviewed the field of synthetic transport systems, particularly ion channels and pores. 

References associated with 1.D.74 family:

Chandrashekar, J., M.A. Hoon, N.J. Ryba, and C.S. Zuker. (2006). The receptors and cells for mammalian taste. Nature 444: 288-294. 17108952
Litvinchuk, S., H. Tanaka, T. Miyatake, D. Pasini, T. Tanaka, G. Bollot, J. Mareda, and S. Matile. (2007). Synthetic pores with reactive signal amplifiers as artificial tongues. Nat Mater 6: 576-580. 17558430
Litvinchuk, S., N. Sordé, and S. Matile. (2005). Sugar sensing with synthetic multifunctional pores. J. Am. Chem. Soc. 127: 9316-9317. 15984828
Matile, S., A. Vargas Jentzsch, J. Montenegro, and A. Fin. (2011). Recent synthetic transport systems. Chem Soc Rev 40: 2453-2474. 21390363
Toko, K. (1998). Electronic tongue. Biosens Bioelectron 13: 701-709. 9828364