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The Bacterial Chloride/Proton Antiporter: A Molecular Machine
Author(s) -
Shan Dan,
Glass Jake,
Hall Ben,
Peters Kyle,
Hardesty Jake
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.lb152
Subject(s) - antiporter , chemistry , chloride , chloride channel , active transport , electrochemical gradient , extracellular , ion transporter , biophysics , membrane , combinatorial chemistry , membrane transport , biochemistry , organic chemistry , biology
E coli has a voltage gated homodimer chloride transporter (ClC‐ec1) that is energized by a proton gradient. The transport of chloride ions is essential for controlling pH levels within a bacterial cell. In the past 10–15 years the crystal structure of CLC‐ec1 has been solved, which led to the realization of how little is known of chloride transport. The Moeller High School CBM SMART Team, working with Dr. Thomas Beck from the University of Cincinnati, used 3‐D modeling and printing technology to examine structure‐function relationships of CLC‐ec1. CLC‐ec1 is part of the Chloride Channel (ClC) family of molecules. The CLC family contains both chloride transporters and chloride channels. The difference being that a transporter is defined by having two ion selectivity gates and a channel having only one. CLC‐ec1 is an antiporter having two voltage gates, 1) a centrally located Tyrosine residue and 2) a Glutamate residue located on the extracellular membrane. These two residues function to block the movement of chloride ions into a cell. CLC‐ec1 exchanges 2 extracellular chloride ions for one intracellular proton. The proton is required to neutralize the slightly negative charge of each of the two gates, creating an environment for Chloride to pass across. CLC‐ec1's primary function is to modulate the pH gradient in E coli. When pH levels in E coli are too low (as occurs on a trip through the stomach) ClC‐ec1 is activated to reverse the pH gradient. To accomplish this CLC‐ec1 uses free energy from the uneven gradients to move protons and chloride ions across its membrane. CLC‐ec1 is homologous in both structure and function to its mammalian counterparts. This gives us a better picture of the functioning of the chloride channel in modulating the transmembrane potential of nerve and muscle cells, the acidification of vesicles, and the alteration of membrane permeability to chloride and other anions. It also leads us to understanding dysfunctional chloride transport, such as occurs in cystic fibrosis and nephrolithiasis. Questions remain, however, about the functioning of the central tyrosine and the mechanism of selectivity for and against other anions.