Signal transduction cascades efficiently transmit chemical and/or physical signals from the extracellular environment to intracellular compartments, thereby eliciting an appropriate cellular response. Most often, these signaling processes are mediated by specific protein-protein interactions involving hundreds of different receptors, enzymes, transcription factors, and signaling, adaptor and scaffolding proteins. Among them, 14-3-3 proteins are a family of highly conserved scaffolding molecules expressed in all eukaryotes, where they modulate the function of other proteins, primarily in a phosphorylation-dependent manner. Through these binding interactions, 14-3-3 proteins participate in key cellular processes, such as cell-cycle control, apoptosis, signal transduction, energy metabolism, and protein trafficking. To date, several hundreds of 14-3-3 binding partners have been identified, including protein kinases, phosphatases, receptors and transcription factors, which have been implicated in the onset of various diseases. As such, 14-3-3 proteins are promising targets for pharmaceutical interventions. However, despite intensive research into their protein-protein interactions, our understanding of the molecular mechanisms whereby 14-3-3 proteins regulate the functions of their binding partners remains insufficient. This review article provides an overview of the current state of the art of the molecular mechanisms whereby 14-3-3 proteins regulate their binding partners, focusing on recent structural studies of 14-3-3 protein complexes.

• Keywords
• 14-3-3 proteins, adaptor protein, molecular mechanism, phosphorylation, protein-protein interactions, scaffolding,
• Publication type
• Journal Article MeSH
• Review MeSH

Neural precursor cells expressed developmentally downregulated protein 4-2 (Nedd4-2), a homologous to the E6-AP carboxyl terminus (HECT) ubiquitin ligase, triggers the endocytosis and degradation of its downstream target molecules by regulating signal transduction through interactions with other targets, including 14-3-3 proteins. In our previous study, we found that 14-3-3 binding induces a structural rearrangement of Nedd4-2 by inhibiting interactions between its structured domains. Here, we used time-resolved fluorescence intensity and anisotropy decay measurements, together with fluorescence quenching and mass spectrometry, to further characterize interactions between Nedd4-2 and 14-3-3 proteins. The results showed that 14-3-3 binding affects the emission properties of AEDANS-labeled WW3, WW4, and, to a lesser extent, WW2 domains, and reduces their mobility, but not those of the WW1 domain, which remains mobile. In contrast, 14-3-3 binding has the opposite effect on the active site of the HECT domain, which is more solvent exposed and mobile in the complexed form than in the apo form of Nedd4-2. Overall, our results suggest that steric hindrance of the WW3 and WW4 domains combined with conformational changes in the catalytic domain may account for the 14-3-3 binding-mediated regulation of Nedd4-2.

• MeSH
• Endosomal Sorting Complexes Required for Transport * metabolism   MeSH
• Catalytic Domain MeSH
• Neural Stem Cells * metabolism   MeSH
• 14-3-3 Proteins metabolism   MeSH
• Nedd4 Ubiquitin Protein Ligases metabolism   MeSH
• Ubiquitin-Protein Ligases metabolism   MeSH
• Protein Binding MeSH
• WW Domains MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Endosomal Sorting Complexes Required for Transport * MeSH
• 14-3-3 Proteins MeSH
• Nedd4 Ubiquitin Protein Ligases MeSH
• Ubiquitin-Protein Ligases MeSH

Translocase of outer mitochondrial membrane 34 (TOMM34) orchestrates heat shock protein 70 (HSP70)/HSP90-mediated transport of mitochondrial precursor proteins. Here, using in vitro phosphorylation and refolding assays, analytical size-exclusion chromatography, and hydrogen/deuterium exchange MS, we found that TOMM34 associates with 14-3-3 proteins after its phosphorylation by protein kinase A (PKA). PKA preferentially targeted two serine residues in TOMM34: Ser93 and Ser160, located in the tetratricopeptide repeat 1 (TPR1) domain and the interdomain linker, respectively. Both of these residues were necessary for efficient 14-3-3 protein binding. We determined that phosphorylation-induced structural changes in TOMM34 are further augmented by binding to 14-3-3, leading to destabilization of TOMM34's secondary structure. We also observed that this interaction with 14-3-3 occludes the TOMM34 interaction interface with ATP-bound HSP70 dimers, which leaves them intact and thereby eliminates an inhibitory effect of TOMM34 on HSP70-mediated refolding in vitro In contrast, we noted that TOMM34 in complex with 14-3-3 could bind HSP90. Both TOMM34 and 14-3-3 participated in cytosolic precursor protein transport mediated by the coordinated activities of HSP70 and HSP90. Our results provide important insights into how PKA-mediated phosphorylation and 14-3-3 binding regulate the availability of TOMM34 for its interaction with HSP70.

• Keywords
• 14-3-3 protein, 70-kDa heat shock protein (Hsp70), HSP70, Hsp70, Tomm34, dimerization, hydrogen-deuterium exchange, molecular chaperone, phosphorylation, protein folding, protein import, protein kinase A (PKA), protein-nucleic acid interaction, protein–protein interaction, translocase of outer mitochondrial membrane 34 (TOMM34),
• MeSH
• DNA-Binding Proteins genetics   metabolism   MeSH
• Phosphorylation physiology   MeSH
• Humans MeSH
• MCF-7 Cells MeSH
• Mitochondrial Precursor Protein Import Complex Proteins MeSH
• Mitochondrial Membranes metabolism   MeSH
• Mitochondrial Proteins metabolism   MeSH
• Molecular Chaperones metabolism   MeSH
• Cyclic AMP-Dependent Protein Kinases metabolism   MeSH
• 14-3-3 Proteins metabolism   MeSH
• HSP70 Heat-Shock Proteins metabolism   MeSH
• HSP72 Heat-Shock Proteins metabolism   MeSH
• HSP90 Heat-Shock Proteins metabolism   MeSH
• Signal Transduction MeSH
• Transcription Factors genetics   metabolism   MeSH
• Mitochondrial Membrane Transport Proteins genetics   metabolism   MeSH
• Protein Binding MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• BCL2-associated athanogene 1 protein MeSH Browser
• DNA-Binding Proteins MeSH
• Mitochondrial Precursor Protein Import Complex Proteins MeSH
• Mitochondrial Proteins MeSH
• Molecular Chaperones MeSH
• Cyclic AMP-Dependent Protein Kinases MeSH
• 14-3-3 Proteins MeSH
• HSP70 Heat-Shock Proteins MeSH
• HSP72 Heat-Shock Proteins MeSH
• HSP90 Heat-Shock Proteins MeSH
• TOMM34 protein, human MeSH Browser
• Transcription Factors MeSH
• Mitochondrial Membrane Transport Proteins MeSH

The limited information available on the structure of complexes involving transcription factors and cognate DNA response elements represents a major obstacle in the quest to understand their mechanism of action at the molecular level. We implemented a concerted structural proteomics approach, which combined hydrogen-deuterium exchange (HDX), quantitative protein-protein and protein-nucleic acid cross-linking (XL), and homology analysis, to model the structure of the complex between the full-length DNA binding domain (DBD) of Forkhead box protein O4 (FOXO4) and its DNA binding element (DBE). The results confirmed that FOXO4-DBD assumes the characteristic forkhead topology shared by these types of transcription factors, but its binding mode differs significantly from those of other members of the family. The results showed that the binding interaction stabilized regions that were rather flexible and disordered in the unbound form. Surprisingly, the conformational effects were not limited only to the interface between bound components, but extended also to distal regions that may be essential to recruiting additional factors to the transcription machinery. In addition to providing valuable new insights into the binding mechanism, this project provided an excellent evaluation of the merits of structural proteomics approaches in the investigation of systems that are not directly amenable to traditional high-resolution techniques.

• Keywords
• DNA, FOXO4, cross-linking, molecular modeling, protein, protein-nucleic acid cross-linking, trans-dichlorodiamineplatinum(II), hydrogen-deuterium exchange, transcription factor, transplatin,
• MeSH
• DNA-Binding Proteins chemistry   metabolism   MeSH
• DNA chemistry   metabolism   MeSH
• Mass Spectrometry MeSH
• Molecular Structure MeSH
• Response Elements MeSH
• Transcription Factors chemistry   metabolism   MeSH
• Deuterium Exchange Measurement MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH
• Names of Substances
• DNA-Binding Proteins MeSH
• DNA MeSH
• Transcription Factors MeSH

Direct interactions between proteins are essential for the regulation of their functions in biological pathways. Targeting the complex network of protein-protein interactions (PPIs) has now been widely recognized as an attractive means to therapeutically intervene in disease states. Even though this is a challenging endeavor and PPIs have long been regarded as "undruggable" targets, the last two decades have seen an increasing number of successful examples of PPI modulators, resulting in growing interest in this field. PPI modulation requires novel approaches and the integrated efforts of multiple disciplines to be a fruitful strategy. This perspective focuses on the hub-protein 14-3-3, which has several hundred identified protein interaction partners, and is therefore involved in a wide range of cellular processes and diseases. Here, we aim to provide an integrated overview of the approaches explored for the modulation of 14-3-3 PPIs and review the examples resulting from these efforts in both inhibiting and stabilizing specific 14-3-3 protein complexes by small molecules, peptide mimetics, and natural products.

• MeSH
• Humans MeSH
• Drug Discovery methods   MeSH
• 14-3-3 Proteins antagonists & inhibitors   metabolism   MeSH
• Protein Stability drug effects   MeSH
• Protein Binding MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Names of Substances
• 14-3-3 Proteins MeSH

Phosducin (Pdc) is a conserved phosphoprotein that, when unphosphorylated, binds with high affinity to the complex of βγ-subunits of G protein transducin (Gtβγ). The ability of Pdc to bind to Gtβγ is inhibited through its phosphorylation at S54 and S73 within the N-terminal domain (Pdc-ND) followed by association with the scaffolding protein 14-3-3. However, the molecular basis for the 14-3-3-dependent inhibition of Pdc binding to Gtβγ is unclear. By using small-angle x-ray scattering, high-resolution NMR spectroscopy, and limited proteolysis coupled with mass spectrometry, we show that phosphorylated Pdc and 14-3-3 form a complex in which the Pdc-ND region 45-80, which forms a part of Pdc's Gtβγ binding surface and contains both phosphorylation sites, is restrained within the central channel of the 14-3-3 dimer, with both 14-3-3 binding motifs simultaneously participating in protein association. The N-terminal part of Pdc-ND is likely located outside the central channel of the 14-3-3 dimer, but Pdc residues 20-30, which are also involved in Gtβγ binding, are positioned close to the surface of the 14-3-3 dimer. The C-terminal domain of Pdc is located outside the central channel and its structure is unaffected by the complex formation. These results indicate that the 14-3-3 protein-mediated inhibition of Pdc binding to Gtβγ is based on steric occlusion of Pdc's Gtβγ binding surface.

• MeSH
• X-Ray Diffraction MeSH
• Phosphoproteins antagonists & inhibitors   chemistry   MeSH
• Phosphorylation MeSH
• Rats MeSH
• Scattering, Small Angle MeSH
• Eye Proteins antagonists & inhibitors   chemistry   MeSH
• Protein Domains MeSH
• 14-3-3 Proteins chemistry   metabolism   MeSH
• GTP-Binding Protein Regulators antagonists & inhibitors   chemistry   MeSH
• Proteolysis MeSH
• Proton Magnetic Resonance Spectroscopy MeSH
• Protein Structure, Secondary MeSH
• Protein Binding MeSH
• Structure-Activity Relationship MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Phosphoproteins MeSH
• Eye Proteins MeSH
• phosducin MeSH Browser
• 14-3-3 Proteins MeSH
• GTP-Binding Protein Regulators MeSH

Apoptosis signal-regulating kinase 1 (ASK1, also known as MAP3K5), a member of the mitogen-activated protein kinase kinase kinase (MAP3K) family, regulates diverse physiological processes. The activity of ASK1 is triggered by various stress stimuli and is involved in the pathogenesis of cancer, neurodegeneration, inflammation, and diabetes. ASK1 forms a high molecular mass complex whose activity is, under non-stress conditions, suppressed through interaction with thioredoxin and the scaffolding protein 14-3-3. The 14-3-3 protein binds to the phosphorylated Ser-966 motif downstream of the ASK1 kinase domain. The role of 14-3-3 in the inhibition of ASK1 has yet to be elucidated. In this study we performed structural analysis of the complex between the ASK1 kinase domain phosphorylated at Ser-966 (pASK1-CD) and the 14-3-3ζ protein. Small angle x-ray scattering (SAXS) measurements and chemical cross-linking revealed that the pASK1-CD·14-3-3ζ complex is dynamic and conformationally heterogeneous. In addition, structural analysis coupled with the results of phosphorus NMR and time-resolved tryptophan fluorescence measurements suggest that 14-3-3ζ interacts with the kinase domain of ASK1 in close proximity to its active site, thus indicating this interaction might block its accessibility and/or affect its conformation.

• Keywords
• 14-3-3 protein, apoptosis signal-regulating kinase 1 (ASK1), fluorescence, nuclear magnetic resonance (NMR), protein cross-linking, small-angle x-ray scattering (SAXS),
• MeSH
• X-Ray Diffraction MeSH
• Phosphorylation MeSH
• Catalytic Domain MeSH
• Humans MeSH
• Scattering, Small Angle MeSH
• MAP Kinase Kinase Kinase 5 antagonists & inhibitors   chemistry   genetics   metabolism   MeSH
• Nuclear Magnetic Resonance, Biomolecular MeSH
• 14-3-3 Proteins chemistry   genetics   metabolism   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• MAP Kinase Kinase Kinase 5 MeSH
• MAP3K5 protein, human MeSH Browser
• 14-3-3 Proteins MeSH
• YWHAE protein, human MeSH Browser