FKBP52 in Neuronal Signaling and Neurodegenerative Diseases: A Microtubule Story.

The FK506-binding protein 52 (FKBP52) belongs to a large family of ubiquitously expressed and highly conserved proteins (FKBPs) that share an FKBP domain and possess Peptidyl-Prolyl Isomerase (PPIase) activity. PPIase activity catalyzes the isomerization of Peptidyl-Prolyl bonds and therefore influences target protein folding and function. FKBP52 is particularly abundant in the nervous system and is partially associated with the microtubule network in different cell types suggesting its implication in microtubule function. Various studies have focused on FKBP52, highlighting its importance in several neuronal microtubule-dependent signaling pathways and its possible implication in neurodegenerative diseases such as tauopathies (i.e., Alzheimer disease) and alpha-synucleinopathies (i.e., Parkinson disease). This review summarizes our current understanding of FKBP52 actions in the microtubule environment, its implication in neuronal signaling and function, its interactions with other members of the FKBPs family and its involvement in neurodegenerative disease.

Bioinspired Hybrid Fluorescent Ligands for the FK1 Domain of FKBP52.

The protein FKBP52 is a steroid hormone receptor coactivator likely involved in neurodegenerative disease. A series of small, water-soluble, bioinspired, pseudopeptidic fluorescent ligands for the FK1 domain of this protein are described. The design is such that engulfing of the ligand in the pocket of this domain is accompanied by hydrogen-bonding of the dansyl chromophore which functions as both an integral part of the ligand and a fluorescent reporter. Binding is concomitant with a significant wavelength shift and an enhancement of the ligand fluorescence signal. Excitation of FK1 domain native tryptophan residues in the presence of bound ligand results in Förster resonance energy transfer. Variation of key ligand residues within the short sequence was undertaken, and the interaction of the resulting library with the protein was measured by techniques including isothermal calorimetry analysis, fluorescence, and FRET quenching, and a range of Kd values were determined. Cocrystallization of a protein ligand complex at 2.30 Å resolution provided detailed information at the atomic scale, while also providing insight into native substrate binding.

The Peptide ERα17p Is a GPER Inverse Agonist that Exerts Antiproliferative Effects in Breast Cancer Cells.

The inhibition of the G protein-coupled estrogen receptor (GPER) offers promising perspectives for the treatment of breast tumors. A peptide corresponding to part of the hinge region/AF2 domain of the human estrogen receptor α (ERα17p, residues 295-311) exerts anti-proliferative effects in various breast cancer cells including those used as triple negative breast cancer (TNBC) models. As preliminary investigations have evoked a role for the GPER in the mechanism of action of this peptide, we focused our studies on this protein using SkBr3 breast cancer cells, which are ideal for GPER evaluation. ERα17p inhibits cell growth by targeting membrane signaling. Identified as a GPER inverse agonist, it co-localizes with GPER and induces the proteasome-dependent downregulation of GPER. It also decreases the level of pEGFR (phosphorylation of epidermal growth factor receptor), pERK1/2 (phosphorylation of extracellular signal-regulated kinase), and c-fos. ERα17p is rapidly distributed in mice after intra-peritoneal injection and is found primarily in the mammary glands. The N-terminal PLMI motif, which presents analogies with the GPER antagonist PBX1, reproduces the effect of the whole ERα17p. Thus, this motif seems to direct the action of the entire peptide, as highlighted by docking and molecular dynamics studies. Consequently, the tetrapeptide PLMI, which can be claimed as the first peptidic GPER disruptor, could open new avenues for specific GPER modulators.

Identification of the Tau phosphorylation pattern that drives its aggregation.

Determining the functional relationship between Tau phosphorylation and aggregation has proven a challenge owing to the multiple potential phosphorylation sites and their clustering in the Tau sequence. We use here in vitro kinase assays combined with NMR spectroscopy as an analytical tool to generate well-characterized phosphorylated Tau samples and show that the combined phosphorylation at the Ser202/Thr205/Ser208 sites, together with absence of phosphorylation at the Ser262 site, yields a Tau sample that readily forms fibers, as observed by thioflavin T fluorescence and electron microscopy. On the basis of conformational analysis of synthetic phosphorylated peptides, we show that aggregation of the samples correlates with destabilization of the turn-like structure defined by phosphorylation of Ser202/Thr205.

A ß-Turn Motif in the Steroid Hormone Receptor's Ligand-Binding Domains Interacts with the Peptidyl-prolyl Isomerase (PPIase) Catalytic Site of the Immunophilin FKBP52.

The immunophilin FKBP52 interacts with nuclear steroid hormone receptors. Studying the crystal structure of human estrogen receptor α (hERα) and using nuclear magnetic resonance, we show here that the short V(364)PGF(367) sequence, which is located within its ligand-binding domain and adopts a type II ß-turn conformation in the protein, binds the peptidyl-prolyl isomerase (PPIase or rotamase) FK1 domain of FKBP52. Interestingly, this turn motif displays strong similarities with the FKBP52 FK1 domain-binding moiety of macrolide immunomodulators such as rapamycin and GPI-1046, an immunophilin ligand with neuroprotective characteristics. An increase in the hydrophobicity of the residue preceding the proline and cyclization of the VPGF peptide strengthen its recognition by the FK1 domain of FKBP52. Replacement of the Pro residue with a dimethylproline also enhances this interaction. Our study not only contributes to a better understanding of how the interaction between the FK1 domain of FKBP52 and steroid hormone receptors most likely works but also opens new avenues for the synthesis of FKBP52 FK1 peptide ligands appropriate for the control of hormone-dependent physiological mechanisms or of the functioning of the Tau protein. Indeed, it has been shown that FKBP52 is involved in the intraneuronal dynamics of the Tau protein.

Application of Circular Dichroism Spectroscopy to the Analysis of the Interaction Between the Estrogen Receptor Alpha and Coactivators: The Case of Calmodulin.

The estrogen receptor α ligand-binding domain (ERα-LBD) binds the natural hormone 17ß-estradiol (E2) to induce transcription and cell proliferation. This process occurs with the contribution of protein and peptide partners (also called coactivators) that can modulate the structure of ERα, and therefore its specificity of action. As with most transcription factors, ERα exhibits a high content of α helix, making it difficult to routinely run spectroscopic studies capable of deciphering the secondary structure of the different partners under binding conditions. Ca(2+)-calmodulin, a protein also highly structured in α-helix, is a key coactivator for ERα activity. Here, we show how circular dichroism can be used to study the interaction of ERα with Ca(2+)-calmodulin. Our approach allows the determination not only of the conformational changes induced upon complex formation but also the dissociation constant (K d) of this interaction.

The sequence Pro295-Thr311 of the hinge region of oestrogen receptor α is involved in ERK1/2 activation via GPR30 in leiomyoma cells.

The ERα (oestrogen receptor α)-derived peptide ERα17p activates rapid signalling events in breast carcinoma cells under steroid-deprived conditions. In the present study, we investigated its effects in ELT3 leiomyoma cells under similar conditions. We show that it activates ERK1/2 (extracellular-signal-regulated kinase 1/2), the Gαi protein, the trans-activation of EGFR (epidermal growth factor receptor) and, finally, cell proliferation. It is partially internalized in cells and induces membrane translocation of ß-arrestins. The activation of ERK1/2 is abolished by the GPR30 (G-protein-coupled receptor 30) antagonist G15 and GPR30 siRNA. When ERα is down-regulated by prolonged treatment with E2 (oestradiol) or specific ERα siRNA, the peptide response is blunted. Thus the simultaneous presence of GPR30 and ERα is required for the action of ERα17p. In addition, its PLM sequence, which interferes with the formation of the ERα-calmodulin complex, appears to be requisite for the phosphorylation of ERK1/2 and cell proliferation. Hence ERα17p is, to our knowledge, the first known peptide targeting ERα-GPR30 membrane cross-talk and the subsequent receptor-mediated biological effects.

A Phosphorylation-Induced Turn Defines the Alzheimer's Disease AT8 Antibody Epitope on the Tau Protein.

Post mortem biochemical staging of Alzheimer's disease is currently based on immunochemical analysis of brain slices with the AT8 antibody. The epitope of AT8 is described around the pSer202/pThr205 region of the hyperphosphorylated form of the neuronal protein tau. In this study, NMR spectroscopy was used to precisely map the AT8 epitope on phosphorylated tau, and derive its defining structural features by a combination of NMR analyses and molecular dynamics. A particular turn conformation is stabilized by a hydrogen bond of the phosphorylated Thr205 residue to the amide proton of Gly207, and is further stabilized by the two Arg residues opposing the pSer202/pThr205.

Concentration-dependent and surface-assisted self-assembly properties of a bioactive estrogen receptor α-derived peptide.

We have synthesized a 17-mer peptide (ERα17p) that is issued from the hinge region of the estrogen receptor α and which activates the proliferation of breast carcinoma cells in steroid-deprived conditions. In the present paper, we show that at a concentration of ~50 µM, it rapidly forms amyloid-like fibrils with the assistance of electrostatic interactions and that at higher concentrations, it spontaneously forms a hydrogel. By using biophysical, spectral and rheological techniques, we have explored the structural, biophysical and mechanical characteristics of ERα17p with respect to fibril formation and gelation.

Bio-inspired nitrile hydration by peptidic ligands based on L-cysteine, L-methionine or L-penicillamine and pyridine-2,6-dicarboxylic acid.

Nitrile hydratase (NHase, EC 4.2.1.84) is a metalloenzyme which catalyses the conversion of nitriles to amides. The high efficiency and broad substrate range of NHase have led to the successful application of this enzyme as a biocatalyst in the industrial syntheses of acrylamide and nicotinamide and in the bioremediation of nitrile waste. Crystal structures of both cobalt(III)- and iron(III)-dependent NHases reveal an unusual metal binding motif made up from six sequential amino acids and comprising two amide nitrogens from the peptide backbone and three cysteine-derived sulfur ligands, each at a different oxidation state (thiolate, sulfenate and sulfinate). Based on the active site geometry revealed by these crystal structures, we have designed a series of small-molecule ligands which integrate essential features of the NHase metal binding motif into a readily accessible peptide environment. We report the synthesis of ligands based on a pyridine-2,6-dicarboxylic acid scaffold and L-cysteine, L-S-methylcysteine, L-methionine or L-penicillamine. These ligands have been combined with cobalt(III) and iron(III) and tested as catalysts for biomimetic nitrile hydration. The highest levels of activity are observed with the L-penicillamine ligand which, in combination with cobalt(III), converts acetonitrile to acetamide at 1.25 turnovers and benzonitrile to benzamide at 1.20 turnovers.

ERα17p, a peptide reproducing the hinge region of the estrogen receptor α associates to biological membranes: A biophysical approach.

Recently, we identified a peptide (ERα17p, P(295)LMIKRSKKNSLALSLT(311)) that corresponds to the 295-311 sequence of the estrogen receptor α (ERα, hinge region) and which exerts a panel of pharmacological effects in breast cancer cells. Remarkably, these effects can result from the interaction of ERα17p with the plasma membrane. Herein, we show that ERα17p adopts a ß-sheet secondary structure when in contact with anionic phospholipids and that it is engulfed within the lipid bilayer. While ERα17p increases the fluidity of membrane mimics, it weakly internalizes in living cells. In light of the above, one may evoke one important role of the 295-311 region of the ERα: the corresponding peptide could be secreted/delivered to the extracellular medium to interact with neighboring cells, both intracellularly and at the membrane level. Finally, the 295-311 region of ERα being in proximity to the cystein-447, the palmitoylation site of the ERα raises the question of its involvement in the interaction/stabilization of the protein with the membrane.

Biophysical studies of the interaction between calmodulin and the R²87-T³¹¹ region of human estrogen receptor α reveals an atypical binding process.

The transcriptional activity of human estrogen receptor ERα is modulated by a number of coregulatory proteins among which calmodulin (CaM). Segment 295-311 in the hinge region of ERα has previously been proposed to be the CaM binding site. In this work, we investigate the molecular mechanism of the interaction of CaM with peptides derived from the hinge region of ERα, using a biophysical approach combining isothermal titration calorimetry, fluorescence, CD and NMR. The ERα17p peptide, corresponding to the previously identified 295-311 region of ERα, recruits mainly the C-terminal domain of Ca(4)CaM, as shown by NMR spectroscopy. In contrast, a longer peptide, ERα25p, extended on the N-terminal side (residues 287-311) interacts with both N- and C-terminal domains of Ca(4)CaM. These results lead to a new delineation of the CaM binding site, encompassing residues 287-294. In particular, fluorescence spectroscopy reveals that the conserved W(292) residue is engaged within hydrophobic pockets on Ca(4)CaM. ITC results show that ERα25p binds Ca(4)CaM with an atypical 2:1 stoichiometry and a dissociation constant in the micromolar range. Based on the NMR titration of Ca(4)CaM by ERα25p showing a biphasic behavior for several residues, we suggest that concerted conformational changes of CaM domains may be required to accommodate the binding of a second peptide. CD spectra indicate that ERα25p partially folds into an α-helix upon binding to Ca(4)CaM. Hence, ERα25p is a new CaM-binding ligand that could be appropriate for the synthesis of derivatives able to control ER-dependent transcription, particularly in the context of hormone-dependent breast tumors.

End-stapled homo and hetero collagen triple helices: a click chemistry approach.

A CuAAC reaction was established for modular synthesis of end-stapled homo- and hetero-triple helical peptides, generating "clicked" macro-assemblies with enhanced thermal stability.