Tryptophan Contributions to the Empirical Free-energy Profile in Gramicidin A/M Heterodimer Channels

Overview

Journal Biophys J

Publisher Cell Press

Specialty Biophysics

Date 2006 Jul 25

PMID 16861266

Citations 3

Authors

Jacob Devin Durrant

Devin Caywood

David D Busath

Affiliations

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Abstract

Gramicidin A/gramicidin M heterodimer conductances were measured in planar lipid bilayers and found to form two distinguishable populations about halfway between the gramicidin A and gramicidin M homodimer conductances. This implies that the principle difference in the gramicidin A and gramicidin M transport free-energy profiles occurs at the channel center, where it would produce similar effects on the rate-limiting barrier for the two heterodimers. Kinetic analysis based on this and nearly all previously published homodimer conductance data for both gramicidin A and gramicidin M channels confirms this conclusion, indicating that the translocation step is approximately 100-fold slower in gramicidin M homodimers than in gramicidin A homodimers and that first- and second-ion exit-rate constants are higher by factors of 24 and 10, respectively. Assuming that the ratios of rate constants are related to the free-energy difference between gramicidin A and gramicidin M, we construct an effective ion-Trp free-energy interaction profile that has a minimum at the channel center.

Citing Articles

The membrane interface dictates different anchor roles for "inner pair" and "outer pair" tryptophan indole rings in gramicidin A channels.

Gu H, Lum K, Kim J, Greathouse D, Andersen O, Koeppe 2nd R Biochemistry. 2011; 50(22):4855-66.

PMID: 21539360 PMC: 3115663. DOI: 10.1021/bi200136e.

Gramicidin channels are internally gated.

Jones T, Fu R, Nielson F, Cross T, Busath D Biophys J. 2010; 98(8):1486-93.

PMID: 20409467 PMC: 2856134. DOI: 10.1016/j.bpj.2009.11.055.

The gramicidin channel ion permeation free-energy profile: direct and indirect effects of CHARMM force field improvements.

Mustafa M, Busath D Interdiscip Sci. 2010; 1(2):113-27.

PMID: 20084184 PMC: 2806686. DOI: 10.1007/s12539-009-0025-3.

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