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

Pilz CS, Steinem C - Eur. Biophys. J. (2008)

Bottom Line: The first two conductance states appear much more prominent demonstrating that the complexation of bipyridine by Ni2+ results in a considerable confinement of the observed multiple conductance states.However, the conductance levels were independent of the presence of Ni2+.Moreover, from a detailed analysis of the open lifetimes of the channels, we conclude that the complexation of Ni2+ diminishes the frequency of channel events with larger open times.

View Article: PubMed Central - PubMed

Affiliation: Institut für Organische und Biomolekulare Chemie, Georg-August Universität, Tammannstr. 2, 37077, Göttingen, Germany.

ABSTRACT
An alpha-helical amphipathic peptide with the sequence H2N-(LSSLLSL)3-CONH2 was obtained by solid phase synthesis and a 2,2'-bipyridine was coupled to its N-terminus, which allows complexation of Ni2+. 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 Ni2+ 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 Ni2+ results in a considerable confinement of the observed multiple conductance states. However, the conductance levels were independent of the presence of Ni2+. Moreover, from a detailed analysis of the open lifetimes of the channels, we conclude that the complexation of Ni2+ diminishes the frequency of channel events with larger open times.

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Synthesis of 3
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Sch1: Synthesis of 3

Mentions: Based on the peptide sequence (1), we attached 8-(4′-methyl-2,2′-bipyridine-4-yl)-octanoic acid (2) to the N-terminus resulting in the receptor functionalized peptide 3 (Scheme 1) to allow for a modulation of the channel activity by complexation of the 2,2′-bipyridines with Ni2+. To prove whether complex formation in the presence of NiCl2 occurs, UV/Vis-spectra of 2 and 3 were taken in ethanol in the absence and presence of NiCl2. 2 shows two π → π* absorption bands at 241 and 282 nm, respectively (Fig. 1a). The presence of equimolar concentrations of Ni2+ leads to a bathochrome shift associated with a splitting of the band at longer wavelengths. This results in three distinct absorption bands at 250, 294, and 305 nm. The found bathochromic shift of the absorption band with a concomitant band splitting in the presence of a metal cation is characteristic for the formation of a Ni2+-2,2′-bipyridine complex (Gilliam et al. 1941; Mason 1968). In Fig. 1b, the absorption spectrum of 3 dissolved in ethanol in the absence of NiCl2 is shown. Only one maximum at 278 nm is discernable, while the second characteristic π → π* absorption band at 240 nm is superimposed by the absorption band of the peptide bonds. Addition of Ni2+ leads to a bathochromic shift, and a splitting into two bands at 291 and 303 nm, which can be attributed to the complexation of the bipyridine functionality by Ni2+.Scheme 1


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

Pilz CS, Steinem C - Eur. Biophys. J. (2008)

Synthesis of 3
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2480505&req=5

Sch1: Synthesis of 3
Mentions: Based on the peptide sequence (1), we attached 8-(4′-methyl-2,2′-bipyridine-4-yl)-octanoic acid (2) to the N-terminus resulting in the receptor functionalized peptide 3 (Scheme 1) to allow for a modulation of the channel activity by complexation of the 2,2′-bipyridines with Ni2+. To prove whether complex formation in the presence of NiCl2 occurs, UV/Vis-spectra of 2 and 3 were taken in ethanol in the absence and presence of NiCl2. 2 shows two π → π* absorption bands at 241 and 282 nm, respectively (Fig. 1a). The presence of equimolar concentrations of Ni2+ leads to a bathochrome shift associated with a splitting of the band at longer wavelengths. This results in three distinct absorption bands at 250, 294, and 305 nm. The found bathochromic shift of the absorption band with a concomitant band splitting in the presence of a metal cation is characteristic for the formation of a Ni2+-2,2′-bipyridine complex (Gilliam et al. 1941; Mason 1968). In Fig. 1b, the absorption spectrum of 3 dissolved in ethanol in the absence of NiCl2 is shown. Only one maximum at 278 nm is discernable, while the second characteristic π → π* absorption band at 240 nm is superimposed by the absorption band of the peptide bonds. Addition of Ni2+ leads to a bathochromic shift, and a splitting into two bands at 291 and 303 nm, which can be attributed to the complexation of the bipyridine functionality by Ni2+.Scheme 1

Bottom Line: The first two conductance states appear much more prominent demonstrating that the complexation of bipyridine by Ni2+ results in a considerable confinement of the observed multiple conductance states.However, the conductance levels were independent of the presence of Ni2+.Moreover, from a detailed analysis of the open lifetimes of the channels, we conclude that the complexation of Ni2+ diminishes the frequency of channel events with larger open times.

View Article: PubMed Central - PubMed

Affiliation: Institut für Organische und Biomolekulare Chemie, Georg-August Universität, Tammannstr. 2, 37077, Göttingen, Germany.

ABSTRACT
An alpha-helical amphipathic peptide with the sequence H2N-(LSSLLSL)3-CONH2 was obtained by solid phase synthesis and a 2,2'-bipyridine was coupled to its N-terminus, which allows complexation of Ni2+. 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 Ni2+ 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 Ni2+ results in a considerable confinement of the observed multiple conductance states. However, the conductance levels were independent of the presence of Ni2+. Moreover, from a detailed analysis of the open lifetimes of the channels, we conclude that the complexation of Ni2+ diminishes the frequency of channel events with larger open times.

Show MeSH