Kinetics of tethering quaternary ammonium compounds to K(+) channels.
Polymeric maleimido-quaternary ammonium (QA) compounds have been shown to function as molecular tape measures when covalently tethered to external cysteine residues of a Shaker K(+) channel (Blaustein R.O., P.A. Cole, C. Williams, and C. Miller. 2000. Nat. Struct. Biol. 7:309-311). For sufficiently long compounds, the cysteine-maleimide tethering reaction creates a high concentration, at the channel's pore, of a TEA-like moiety that irreversibly blocks current. This paper investigates a striking feature of the maleimide-cysteine tethering kinetics. Strong blockers-those that induce substantial levels (>80%) of irreversible inhibition of current-react with channel cysteines much more rapidly than weak blockers and, when delivered to channels with four cysteine targets, react with multiexponential kinetics. This behavior is shown to arise from the ability of a strong blocker to concentrate its maleimide end near a channel's cysteine target by exploiting the reversible pore-blocking affinity of its QA headgroup.
Blaustein
Robert O
RO
Department of Biochemistry, Brandeis University, Waltham, MA 02454, USA. robert.blaustein@tufts.edu
D000818:Animals; D003545:Cysteine / Q000378:metabolism; D007700:Kinetics; D008301:Maleimides / Q000378:metabolism; D009865:Oocytes; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D051637:Shaker Superfamily of Potassium Channels; D019789:Tetraethylammonium / Q000378:metabolism; D014981:Xenopus
D008301:Maleimides; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D000644:Quaternary Ammonium Compounds; D051637:Shaker Superfamily of Potassium Channels; C043592:maleimide; D019789:Tetraethylammonium; D003545:Cysteine