Can Ag Permeate through a Potassium Ion Channel? A Bottom-Up Approach by Infrared Spectroscopy of the Ag Complex with the Partial Peptide of a Selectivity Filter.

Silver and silver ions have a long history of antimicrobial activity and medical applications. Nevertheless, the activity of Ag against bacteria, how it enters a cell, has not yet been established. The K channel, a membrane protein, is a possible route. The addition of a channel inhibitor (4-aminopyridine) to modulate the Ag uptake could support this view. However, the inhibitor enhances the uptake of Ag, the opposite result. We have applied cold ion trap infrared laser spectroscopy to complexes of Ag and Ac-Tyr-NHMe (a model for GYG) which is a portion of the selectivity filter in the K channel to consider the question of permeation. With support from quantum chemical calculations, we have determined the stable conformations of the complex. The conformations strongly suggest that Ag would not readily permeate the K channel. The mechanism of the unexpected enhancement by the inhibitor is discussed.