A high-conductance cation channel from the inner membrane of the free-living soil bacteria Rhizobium etli
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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 P Rb/P K = 0.96, P Na/P K = 0.07, and a conductance ratio of γRb/γK = 1.1. The channel here characterized represents a previously undescribed Rhizobium channel although its precise role in rhizobial physiology remains yet to be determined.
KeywordsRhizobium Ion channels Permeation
We thank Guadalupe Zavala for her excellent technical assistance with electron microscopy and to Karla García y García for helping us with database searching using RetliDB. This work was supported by Grants CONACyT 56631 and DGAPA IN204907 to C.Q. and CONACyT 60313 and DGAPA IN222208 to F.G.L. D. Balleza thanks to DGAPA-UNAM for a postdoctoral fellowship. We sincerely thank the reviewers for their insightful comments and suggestions.
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