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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. KEY WORDS: Shaker * tetraethylammonium * block * affinity-label * maleimide

A study of the characteristics of ezrin by comparing the effects of the overexpression of the full coding sequence 1-586 of the human membrane cytoskeletal linker ezrin with that of the 1-233 NH2-terminal domain and the 310-586 COOH-terminal domain in insect cells reveals that cell adhesion of infected Sf9 cells is increased by both the 1-586 and 1-233 sequences, without any severe morphological alterations in the cell structures. Ezrin 310-586 leads to microspike and lamellipodia extensions through Sf 9 cell actin mobilization, following membrane spreading and cell adhesion enhancement. Videomicroscopic and drug-interference studies reveal that tubulin assembly is mediated by actin mobilization.

The potassium-selective ion channel blocker tetraethylammonium ion (TEA) blocks chlorate-selective ion channels, causing the closure of the channel passing through the open state. The closure is due to reduction in channel conductance and time averaging of extremely fast blocking and unblocking transitions. Rapid blocking and unblocking transitions cause apparent decrease in single-channel current amplitude. Unlike delayed rectifier channels, fast C1 channels are blocked with higher affinity by long chain quaternary ammonium compounds.