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Updated: Jul 9, 2026
07:47
A Proteoliposome-Based Efflux Assay to Determine Single-molecule Properties of Cl- Channels and Transporters
Published on: April 20, 2015
CLC Cl /H+ transporters constrained by covalent cross-linking
Wang Nguitragool1, Christopher Miller
1Department of Biochemistry, Howard Hughes Medical Institute and Brandeis University, Waltham, MA 02454, USA.
Summary
This study investigated chloride-proton (Cl-/H+) exchangers by covalently linking subunits of a bacterial CLC exchanger. Results suggest individual subunits function independently, not requiring large structural changes for ion transport.
Area of Science:
- Biochemistry
- Molecular Biology
- Structural Biology
Background:
- Chloride-proton (Cl-/H+) exchangers are homodimers, but the role of inter-subunit interactions in their transport mechanism remains unclear.
- It is unknown if subunits rearrange conformationally or function independently during ion transport.
Purpose of the Study:
- To investigate the quaternary structural requirements for CLC exchanger function.
- To determine if CLC exchangers require large conformational changes between subunits for ion transport.
Main Methods:
- Cysteine substitution mutants were engineered in a cysteine-less background of the bacterial CLC-ec1 exchanger.
- Subunits were covalently linked using disulfide or cysteine-lysine cross-bridges.
- Cross-linked proteins were reconstituted and functionally assessed for ion transport activity.
Main Results:
- Constructs with one, two, or four cross-bridges remained functionally active.
- Cross-linked exchangers exhibited competent Cl(-) turnover rates and Cl(-)/H(+) exchange stoichiometry.
- H(+) pumping driven by a Cl(-) gradient was preserved in cross-linked constructs.
Conclusions:
- Large quaternary rearrangements are not essential for the ion transport cycle in CLC exchangers.
- The transport mechanism is likely carried out by individual subunits operating independently, similar to 'fast gating' in CLC channels.
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