Conformational changes required for H(+)/Cl(-) exchange mediated by a CLC transporter.

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Chloride channel exchangers (CLCs) are crucial for transmembrane chloride transport.
• Mutations in CLCs are linked to various genetic disorders, yet their transport mechanism is unclear.
• Conventional models propose two gates, but CLCs were thought to have only one.

Purpose of the Study:

• To elucidate the transport mechanism of CLC-type exchangers.
• To investigate the role of helix O movements in CLC transport.
• To challenge the existing models of CLC function.

Main Methods:

• Utilized cross-linking strategies to constrain helix O movements in CLC-ec1.
• Determined the structure of cross-linked CLC-ec1 using techniques like X-ray crystallography.
• Analyzed the structural and functional consequences of helix O constraint.

Main Results:

• Cross-linking helix O inhibited transport while maintaining a native-like structure.
• Helix O movements are coupled to the ion pathway via a specific C-terminal contact.
• Identified a two-gate mechanism in CLCs involving conformational changes outside the ion pathway.

Conclusions:

• CLC exchangers operate via a nonconventional two-gate mechanism.
• Conformational changes in helix O, distant from the ion pathway, regulate transport.
• This provides a new framework for understanding CLC function and associated diseases.