Figure 4.

Effects of MTSET and NEM at sites in the β-barrel transmembrane domain of the anthrax channel. Upper left is a secondary structure diagram of a β-hairpin from a single subunit, modified from Nassi et al. (2002). Residues sensitive to MTSET are indicated by solid black arrowheads, insensitive residues by unfilled arrowheads, and those not tested by open circles. Residue numbers for sites examined in this paper are shown in bold and larger type. Currents were elicited by 1-s pulses to +60 mV, followed by 10-s pulses to −60 mV. Baseline current traces before exposure to MTSET or NEM are depicted by dotted lines; traces obtained after exposure to reagent are superimposed at the same scale (solid black lines) and after normalizing to the peak currents at −60 mV before reaction (gray) to emphasize effects on gating. At all sites tested, except for F313C, MTSET exposure eliminated gating and had a significant effect on current (range, 25–98% decrease). NEM decreased conductance at many sites tested (range, 15–95% decrease) but had no effect on gating. Results are representative of three to six experiments with each reagent at each site.