The 14-3-3 proteins are a family of regulatory signaling molecules that interact with other proteins in a phosphorylation-dependent manner. 14-3-3 proteins are thought to play a direct role in the regulation of subcellular localization of FoxO forkhead transcription factors. It has been suggested that the interaction with the 14-3-3 protein affects FoxO binding to the target DNA and interferes with the function of nuclear localization sequence (NLS). Masking or obscuring of NLS could inhibit interaction between FoxO factors and nuclear importing machinery and thus shift the equilibrium of FoxO localization toward the cytoplasm. According to our best knowledge, there is no experimental evidence showing a direct interaction between the 14-3-3 protein and NLS of FoxO. Therefore, the main goal of this work was to investigate whether the phosphorylation by protein kinase B, the 14-3-3 protein, and DNA binding affect the structure of FoxO4 NLS. We have used site-directed labeling of FoxO4 NLS with the extrinsic fluorophore 1,5-IAEDANS in conjunction with steady-state and time-resolved fluorescence spectroscopy to study conformational changes of FoxO4 NLS in vitro. Our data show that the 14-3-3 protein binding significantly changes the environment around AEDANS-labeled NLS and reduces its flexibility. On the other hand, the phosphorylation itself and the binding of double-stranded DNA have a small effect on the structure of this region. Our results also suggest that the DNA-binding domain of FoxO4 remains relatively mobile while bound to the 14-3-3 protein.

Institute of Physiology Academy of Sciences of the Czech Republic 12843 Prague Czech Republic

References provided by Crossref.org

Isotopic Depletion Increases the Spatial Resolution of FPOP Top-Down Mass Spectrometry Analysis

Structural insights into the functional roles of 14-3-3 proteins

Structural basis for SARS-CoV-2 nucleocapsid (N) protein recognition by 14-3-3 proteins

Forkhead Domains of FOXO Transcription Factors Differ in both Overall Conformation and Dynamics

Phosphatidylinositol 4-kinase IIIβ (PI4KB) forms highly flexible heterocomplexes that include ACBD3, 14-3-3, and Rab11 proteins

Crystal structures of a yeast 14-3-3 protein from Lachancea thermotolerans in the unliganded form and bound to a human lipid kinase PI4KB-derived peptide reveal high evolutionary conservation

Structural modulation of phosducin by phosphorylation and 14-3-3 protein binding

Structural basis for the 14-3-3 protein-dependent inhibition of the regulator of G protein signaling 3 (RGS3) function