Blocker efflux through blocked pores

The objective of this paper is to clarify a frequent confusion that occurs with synthetic multifunctional pores: does molecular recognition by a synthetic pore exclude molecular translocation through the same pore? Evidence that this is not the case is provided with a set of competitive experiments using a rigid-rod s-barrel with internal histidine-arginine dyads as synthetic multifunctional pores (SMPs) as well as 8-hydroxypyrene-1,3,6-trisulfonate (HPTS) as a fluorescent and 1,3,6,8-pyrenetetrasulfonate (PTS) as a non-fluorescent blocker. Direct evidence for the efflux of HPTS blockers through blocked SMPs is obtained by quenching of released HPTS with an externally added quencher. Blockage of blocker efflux through blocked pores was demonstrated by adding PTS as the opposing external blocker (KD = 3.3 µM). A Hill coefficient of n = 1.5 may indicate that binding of more than one PTS blocker is necessary to inhibit the efflux of HPTS blockers. Supported by structural information on blockage and selectivity from biological potassium channels, blocker efflux through blocked pores is discussed as being implicated in selectivity.