Anomalous proton selectivity in a large channel: colicin A
Stephen L Slatin1, Alan Finkelstein, Paul K Kienker
1Department of Physiology and Biophysics, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, USA. slatin@aecom.yu.edu
Biochemistry
|January 22, 2008
Summary
Colicin channels, particularly colicin A, exhibit remarkable proton selectivity despite their large size. This unexpected finding challenges current models of ion permeation through protein channels.
Area of Science:
- Biochemistry
- Molecular Biology
- Biophysics
Background:
- Bactericidal proteins called colicins form channels in bacterial membranes.
- These channels conduct ions but have unexpectedly low conductance for their size.
- The precise structure and ion permeation mechanism of colicin channels remain unclear.
Purpose of the Study:
- To investigate the ion selectivity of the colicin A channel.
- To reconcile the observed proton selectivity with the channel's large diameter.
- To propose a novel mechanism for ion permeation in colicin channels.
Main Methods:
- Reversal potential measurements across planar lipid bilayers.
- Utilizing pH gradients to assess ion selectivity.
- Re-evaluation of colicin channel lumen diameter.
Main Results:
- Colicin A channels demonstrate high selectivity for protons over other ions.
- Observed proton selectivity is orders of magnitude greater than expected for a 10 Å channel.
- Experimental data contradicts current models of channel permeation.
Conclusions:
- Colicin channels employ an unconventional mechanism for ion permeation.
- The large diameter does not preclude significant proton selectivity.
- Further research is needed to elucidate this unorthodox mechanism.
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