Aquaporin-0 Interacts with the FERM Domain of Ezrin/Radixin/Moesin Proteins in the Ocular Lens

Abstract

Aquaporin 0 (AQP0) is the major intrinsic protein in the lens and is essential for establishing proper fiber cell structure and organization. Cytoskeletal proteins that directly interact with the C terminus of AQP0 are identified herein. The water-insoluble fraction of lens fiber cells was chemically cross-linked, and cross-linked peptides with the C terminus of AQP0 were identified by mass spectrometry. Coimmunoprecipitation and AQP0 C-terminal peptide pulldown experiments were used to confirm the protein-protein interaction. Unexpectedly, AQP0 was found to directly associate with ezrin/radixin/moesin (ERM) family members, proteins that are involved in linkage of actin filaments to the plasma membrane. Cross-linked peptides were detected between AQP0 and degenerate sequences of ezrin and radixin; however, AQP0 interaction with ezrin is believed to play a more significant function in the lens because of its higher level of expression and observed ezrin-specific cross-linking. The interaction was found to occur between the C terminus of AQP0 and subdomains F1 and F3 of ERM proteins. The interaction between AQP0 and ezrin was confirmed by coimmunoprecipitation and AQP0 C-terminal peptide pulldown experiments. Considering the important known functions of the cellular actin cytoskeleton in fiber cell differentiation, the interaction of AQP0 and ERM proteins may play an important role in fiber cell morphology, elongation, and organization.