Microfluidic formation of lipid bilayer array for membrane transport analysis

How do small hydrophilic nonelectrolytes cross cell membranes? Which pathways are most important for small lipid insoluble molecules to cross cell membranes? These are questions that have been basic to membrane transport physiology for decades. More importantly, these are questions whose answers have changed significantly within the last 10 years. This review discusses the evidence that pathways other than the lipid bilayer itself exist for the transport across cell membranes of specific small hydrophilic nonelectrolytes. The description begins with briefly analyzing the relevance of well accepted basic mathematical models for transport for understanding the permeability of representative physiologically important molecules across actual cell membranes. Particular emphasis is placed on describing recently discovered proteins that facilitate the transport of some of the smallest physiologically important lipid-insoluble molecules, water, and urea. Evidence also exists for transport proteins that selectively enhance the transmembrane transport of other small lipid-insoluble molecules. Do nonselective pores for small molecules exist in cell membranes?

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Fluorescent Measurement of Membrane Transport Using Artificial Lipid Bilayer Microchambers

JAPANESE JOURNAL OF MULTIPHASE FLOW ◽

10.3811/jjmf.2020.t008 ◽

2020 ◽

Vol 34 (2) ◽

pp. 326-333

Author(s):

Taishi TONOOKA

Keyword(s):

Membrane Transport ◽

Lipid Bilayer

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Fluoride resistance and transport by riboswitch-controlled CLC antiporters

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1210896109 ◽

2012 ◽

Vol 109 (38) ◽

pp. 15289-15294 ◽

Cited By ~ 68

Author(s):

Randy B. Stockbridge ◽

Hyun-Ho Lim ◽

Renee Otten ◽

Carole Williams ◽

Tania Shane ◽

...

Keyword(s):

Escherichia Coli ◽

Binding Site ◽

Membrane Transport ◽

Lipid Bilayer ◽

Anion Binding ◽

Planar Lipid Bilayer ◽

Sequence Alignments ◽

Conserved Residues ◽

Anion Selectivity ◽

Osmotic Response

A subclass of bacterial CLC anion-transporting proteins, phylogenetically distant from long-studied CLCs, was recently shown to be specifically up-regulated by F-. We establish here that a set of randomly selected representatives from this “CLCF” clade protect Escherichia coli from F- toxicity, and that the purified proteins catalyze transport of F- in liposomes. Sequence alignments and membrane transport experiments using 19F NMR, osmotic response assays, and planar lipid bilayer recordings reveal four mechanistic traits that set CLCF proteins apart from all other known CLCs. First, CLCFs lack conserved residues that form the anion binding site in canonical CLCs. Second, CLCFs exhibit high anion selectivity for F- over Cl-. Third, at a residue thought to distinguish CLC channels and transporters, CLCFs bear a channel-like valine rather than a transporter-like glutamate, and yet are F-/H+ antiporters. Finally, F-/H+ exchange occurs with 1∶1 stoichiometry, in contrast to the usual value of 2∶1.

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