A high-conductance cation channel from the inner membrane of the free-living soil bacteria Rhizobium etli
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SHORT COMMUNICATION
A high-conductance cation channel from the inner membrane of the free-living soil bacteria Rhizobium etli Daniel Balleza • Carmen Quinto • David Elias Froyla´n Go´mez-Lagunas
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Received: 12 December 2009 / Revised: 29 April 2010 / Accepted: 10 May 2010 / Published online: 26 May 2010 Ó Springer-Verlag 2010
Abstract In this communication we reported the study of a cation channel present in the cytoplasmic membrane of the nitrogen fixing bacterium Rhizobium etli. Inner-membrane (IM) vesicles were purified and fused into planar lipid bilayers (PLBs), under voltage clamp conditions. We have found that fusion of IM-enriched vesicle fractions with these model membranes leads, mainly ([30% of 46 experiments), to the reconstitution of high-conductance channels. Following this strategy, the activity of a channel with main open conductance of 198 pS, in symmetrical 100 mM KCl, was recorded. The single-channel
conductance increase to 653 pS in the presence of a 5:1 (cis to trans) gradient of KCl. The channel exhibits voltage dependency and a weak selectivity for cations showing a permeability ratios of PRb/PK = 0.96, PNa/PK = 0.07, and a conductance ratio of cRb/cK = 1.1. The channel here characterized represents a previously undescribed Rhizobium channel although its precise role in rhizobial physiology remains yet to be determined. Keywords
Rhizobium Ion channels Permeation
Introduction Communicated by Ursula Priefer.
Electronic supplementary material The online version of this article (doi:10.1007/s00203-010-0587-3) contains supplementary material, which is available to authorized users. D. Balleza C. Quinto Departamento de Biologı´a Molecular de Plantas, Instituto de Biotecnologı´a, UNAM, Ap. Postal 510-3, Cuernavaca, Morelos 62210, Mexico D. Elias Departamento de Fisiologı´a, Biofı´sica y Neurociencias. CINVESTAV-IPN, Av. IPN 2508, Col. Zacatenco, Mexico City CP 07300, Mexico F. Go´mez-Lagunas (&) Facultad de Medicina, Departamento de Fisiologı´a, UNAM. Me´xico. Cd. Universitaria, Ap. Postal 70-250, Me´xico, D.F. 04510, Mexico e-mail: [email protected] Present Address: D. Balleza (&) Unidad de Biofı´sica, CSIC-UPV/EHU, Universidad del Paı´s Vasco, Barrio Sarriena s/n, 48940 Leioa, Spain e-mail: [email protected]
Ion channels are ubiquitous transport proteins that allow the passive flux of ions across membranes and participate in a great variety of physiological processes. Regarding unicellular organisms, the type and physiological roles of the ion channels that they express are of particular interest. One way in which free-living single cells face the changing, and in many cases extreme environmental conditions they find, is by expressing particular transport proteins that help them to fulfil their physiological requirements in a given particular condition. Some examples of this are wellstudied ion channels reported in the literature. For example, in yeast, the expression of two K? carrier systems of different affinity plus a K? channel allows the cells to achieve the appropriate
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