Structural Basis for the Interaction between the Ezrin FERM-Domain and Human Aquaporins

Area of Science:

• Cell Biology
• Biochemistry
• Structural Biology

Background:

• The Ezrin/Radixin/Moesin (ERM) protein family connects the plasma membrane to the actin cytoskeleton.
• This interaction is vital for cell polarization, morphogenesis, adhesion, and protein trafficking.
• ERM proteins, specifically the FERM domain, are known to interact with aquaporin (AQP) C-termini, influencing AQP plasma membrane localization.

Purpose of the Study:

• To investigate the structural basis of the interaction between ezrin and human aquaporins AQP2 and AQP5.
• To elucidate the binding mechanism and affinities involved in these protein interactions.

Main Methods:

• Microscale thermophoresis was used to determine the binding affinities between ezrin's FERM domain and AQP2/AQP5.
• ColabFold was employed for molecular modeling to visualize the complex structures of FERM-AQP2 and FERM-AQP5.

Main Results:

• Both full-length AQP2/AQP5 and their C-terminal peptides bind to the ezrin FERM domain with low micromolar affinities.
• Structural modeling revealed a common binding mode where both proximal and distal AQP C-termini simultaneously engage distinct FERM domain sites.
• This dual-site binding mode, while similar at individual sites to other FERM complexes, is novel in its concurrent engagement and differs from known auto-inhibitory mechanisms.

Conclusions:

• Ezrin and AQP2/AQP5 exhibit a novel binding mode involving simultaneous interaction with distinct sites on the ezrin FERM domain.
• This interaction is critical for the proper localization of AQP2 and AQP5 in the plasma membrane.
• The findings expand our understanding of ERM protein interactions with extrinsic partners.