PH-Regulated Nonelectrogenic Anion Transport by Phenylthiosemicarbazones.

Ethan N W Howe,Dawid D Czech,Mark E Light,Stuart N Berry,Jonathan A Kitchen,Philip A Gale,Harry A Klein,Xin Wu,Nathalie Busschaert,Junming Ho

doi:10.1021/jacs.6b04656

Abstract

Gated ion transport across biological membranes is an intrinsic process regulated by protein channels. Synthetic anion carriers (anionophores) have potential applications in biological research; however, previously reported examples are mostly nonspecific, capable of mediating both electrogenic and electroneutral (nonelectrogenic) transport processes. Here we show the transmembrane Cl(-) transport studies of synthetic phenylthiosemicarbazones mimicking the function of acid-sensing (proton-gated) ion channels. These anionophores have remarkable pH-switchable transport properties with up to 640-fold increase in transport efficacy on going from pH 7.2 to 4.0. This "gated" process is triggered by protonation of the imino nitrogen and concomitant conformational change of the anion-binding thiourea moiety from anti to syn. By using a combination of two cationophore-coupled transport assays, with either monensin or valinomycin, we have elucidated the fundamental transport mechanism of phenylthiosemicarbazones which is shown to be nonelectrogenic, inseparable H(+)/Cl(-) cotransport. This study demonstrates the first examples of pH-switchable nonelectrogenic anion transporters.

Highlights

Transmembrane ion transport processes facilitated by protein channels and carriers across biological lipid bilayer membranes are essential for life.[1]
We have previously shown that this is because simple neutral hydrogen bonding anionophores such as 7 are nonspecific and can function both as an electrogenic chloride transporter that can couple with valinomycin and as a H+ transporter or functionally equivalent OH− transporter; these processes together with Cl− transport can couple with the electroneutral K+/H+ transport by monensin.[19]
We have shown that phenylthiosemicarbazones are the first examples of nonelectrogenic anion transporters that show pHswitching behavior between neutral and acidic pH conditions

Summary

■ INTRODUCTION

Transmembrane ion transport processes facilitated by protein channels and carriers across biological lipid bilayer membranes are essential for life.[1]. In collaboration with Jolliffe and co-workers, has previously reported thiosquaramides and an oxothiosquaramide as pH-dependent anionophores.[12] these carriers can mediate electrogenic transport and are capable of depolarizing the membrane potential;[13] this is undesirable for certain cellular studies.[14] The challenge is to develop pH-switchable anionophores with truly prodigiosin-like transport properties.

■ RESULTS AND DISCUSSION

■ CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES