Modulation of the conductance of a 2,2′-bipyridine-functionalized peptidic ion channel by Ni2+

An alpha-helical amphipathic peptide with the sequence H(2)N-(LSSLLSL)(3)-CONH(2) was obtained by solid phase synthesis and a 2,2'-bipyridine was coupled to its N-terminus, which allows complexation of Ni(2+). Complexation of the 2,2'-bipyridine residues was proven by UV/Vis spectroscopy. The peptide helices were inserted into lipid bilayers (nano black lipid membranes, nano-BLMs) that suspend the pores of porous alumina substrates with a pore diameter of 60 nm by applying a potential difference. From single channel recordings, we were able to distinguish four distinct conductance states, which we attribute to an increasing number of peptide helices participating in the conducting helix bundle. Addition of Ni(2+) in micromolar concentrations altered the conductance behaviour of the formed ion channels in nano-BLMs considerably. The first two conductance states appear much more prominent demonstrating that the complexation of bipyridine by Ni(2+) results in a considerable confinement of the observed multiple conductance states. However, the conductance levels were independent of the presence of Ni(2+). Moreover, from a detailed analysis of the open lifetimes of the channels, we conclude that the complexation of Ni(2+) diminishes the frequency of channel events with larger open times.