Trifluoperazine Binding Research Articles

Highly conserved protein Rv1211 in Mycobacterium tuberculosis is a natively unfolded protein that binds to a calmodulin antagonist, trifluoperazine

Rv1211 is a conserved hypothetical protein in Mycobacterium tuberculosis and is required for the growth and pathogenesis of the bacteria. The protein has been suggested as a calmodulin-like calcium-binding protein with an EF-hand motif and as a target of trifluoperazine, a calmodulin antagonist in eukaryotes that inhibits mycobacterial growth. Here, we expressed the recombinant protein of Rv1211 and performed structural and biochemical studies of Rv1211 and its interaction with Ca2+ or trifluoperazine. Surprisingly, Rv1211 exhibited an elution property typical of a natively unfolded protein. Subsequent circular dichroism experiments with temperature elevation and trifluoroethanol treatment showed that Rv1211 has unfolded structure. Additional NMR experiment confirmed the unfolded state of the protein and further showed that it does not bind to Ca2+. Still, Rv1211 did bind to trifluoperazine, as evidenced by the two-dimensional NMR spectra of 15N-labeled Rv1211. However, there were no peak shifts upon binding, showing that Rv1211 retained its unfolded state even after the trifluoperazine binding. The residues involved in the binding were clustered in the C-terminal region, as identified by the sequence assignment. Isothermal titration calorimetry showed that the Kd of trifluoperazine-Rv1211 binding is 41 μM and that the stoichiometry is 1 : 2 (Rv1211: trifluoperazine). Our results argue against the suggestion of Rv1211 as a Ca2+-binding calmodulin-like protein, and show that Rv1211 is a natively unfolded protein that binds to trifluoperazine. In addition, our results suggest the evidence of the “Fuzziness” in the Rv1211-trifluoperazine interaction that differs from the conventional binding-induced folding of natively unfolded proteins.

Molecular Interaction Site on Procoagulant Skeletal Muscle Myosin for Factor Xa-Dependent Prothrombin Activation

Skeletal muscle myosin (SkM) is a muscle protein consisting of a dimer of heterotrimers, each trimer comprising a regulatory light chain (RLC), an essential light chain (ELC), and a heavy chain (HC). Recently it was discovered that SkM has potent procoagulant and prothrombotic activity (Deguchi H, et al, Blood. 2016;128:1870-1878). Mechanistic studies showed that SkM's potent prothrombotic activity involved enhancing thrombin generation due to SkM's ability to bind coagulation factors Xa and Va which accelerates prothrombin activation. However, detailed molecular mechanisms for SkM's binding of these coagulation factors have not been described. Since a well-known myosin inhibitor, trifluoperazine (TFP), inhibited SkM's procoagulant activity and since this inhibitor binds to the ELC in SkM's "neck" region which connects the HC head region to the HC tail (Figure, panel A), we hypothesized that SkM's TFP binding region on the ELC in the neck region directly contributes to SkM's procoagulant activity. To identify potential binding site(s) on SkM for factors Xa and Va, 22 peptides representing the neck region's RLC, ELC, and HC were screened for inhibition of SkM-supported prothrombin activation by purified factor Xa, factor Va, and calcium ions. These peptides contained 25-40 residues and overlapped by approximately 5-10 amino acids. Peptides ELC109-138 and ELC129-159, corresponding to amino acid residues 109-138 and 129-159 of the ELC, inhibited SkM-supported prothrombin activation at 100 μM, whereas their partially overlapping neighboring peptides, ELC99-122 and ELC149-173, did not. Three HC peptides (peptides HC781-810, HC796-835, HC815-854) and one RLC peptide (RLC133-162) inhibited SkM-supported prothrombin activation at 100 μM, and each was also inhibitory, to varying degrees, when assayed at 5 μM. Dose-dependency inhibition assays gave IC50 values (50% inhibition of activity) for the peptides HC781-810, HC796-835, HC815-854, and RLC133-162 of 64, 1.2, 2.3 and 26 μM. Peptides HC781-810 and HC815-854 also inhibited prothrombin activation in the absence of myosin but in the presence of phospholipid vesicles containing 20 % phosphatidylserine (IC50 = 7.5 and 104 μM, respectively). In contrast, the strong inhibitory effects of peptides HC796-835, RLC133-162, ELC109-138 and ELC129-159 seen in the presence of myosin were not at all apparent in the presence of phospholipid-supported prothrombin activation when myosin was absent. This suggests that peptides HC796-835, RLC133-162, ELC109-138 and ELC129-159 specifically inhibit SkM-supported prothrombin activation. The 19 synthetic peptides representing the SkM neck region were also screened at 25 µM (final) for their inhibition of recalcification-induced thrombin generation in human plasma which contains significant circulating levels of SkM. Among the 19 peptides tested, HC796-835 and HC815-854 significantly inhibited thrombin generation when screened at 25 µM in plasma. Immobilized peptide HC796-835 showed direct binding of purified factor Xa with apparent Kd of 1.4 μM. This very potent inhibitory peptide, HC796-835, exhibited 50% inhibition of SkM-enhanced prothrombin activation at 1.2 μM, indicating that this peptide's sequence provides a factor Xa binding site on SkM which contributes to its inhibitory action. More specifically, an overlapping peptide containing amino acid residues 815-835 inhibited SkM-enhanced prothrombin activation by factors Xa and Va while a peptide comprising residues 796-811 did not. These studies suggest that residues 815-835 of SkM's HC are responsible for directly binding factor Xa and implies that this binding is responsible for SkM's procoagulant activity (Figure, panel B). In summary, we identified human SkM peptides which specifically blocked SkM-enhanced thrombin generation but not phospholipid-stimulated prothrombin activation in purified reaction mixtures and which inhibited blood clotting in plasma. The most potent anticoagulant HC peptide also directly binds purified factor Xa. These findings strongly suggest that the neck region of SkM, as defined by these inhibitory peptides (Figure, panel B), provides a phospholipid-independent procoagulant surface for thrombin generation that, depending on the in vivo physiologic context, may contribute to either hemostasis or thrombosis. Figure Disclosures No relevant conflicts of interest to declare.

Characterizing the interactions of the antipsychotic drug trifluoperazine with bovine serum albumin: Probing the drug-protein and drug-drug interactions using multi-spectroscopic approaches

Trifluoperazine is a potent antipsychotic drug used in the treatment of neurological disorders. The usage of trifluoperazine is often found to be associated with more adverse side effects as compared to other low-potency antipsychotic agents. Plasma proteins play an inevitable role in determining the pharmacokinetic properties of a drug. Hence, this study was conducted with an aim to characterize the interactions of trifluoperazine with bovine serum albumin and determine the influence of other small molecules on its interaction with serum albumin. Trifluoperazine bound to BSA at two independent sites with Kd values of 9.5 and 172.6 μM. Förster resonance energy transfer and computational docking analysis revealed that both the binding sites of trifluoperazine were located closer to TRP 213 in subdomain IIA of BSA. Evaluation of trifluoperazine-BSA interactions at three different temperatures indicated that there was a stable complex formation between the two molecules at the ground state and that the static quenching mechanism was predominant behind these interactions. Binding studies in the presence of pharmaceutically relevant drugs indicated that warfarin, paracetamol, and caffeine negatively influenced the binding of trifluoperazine on BSA. Lastly, Fourier transformed infrared spectroscopy and circular dichroism spectroscopy indicated that the binding of trifluoperazine induced a conformational change by reducing the α-helical content of BSA. The study implicates that the small molecules which prefer binding to the Sudlow site I of BSA might compete with trifluoperazine for its binding site thereby increasing the concentration of free trifluoperazine in the plasma which could lead to adverse side effects in patients.

Trifluoperazine, a Well-Known Antipsychotic, Inhibits Glioblastoma Invasion by Binding to Calmodulin and Disinhibiting Calcium Release Channel IP3R

Calcium (Ca2+) signaling is an important signaling process, implicated in cancer cell proliferation and motility of the deadly glioblastomas that aggressively invade neighboring brain tissue. We have previously demonstrated that caffeine blocks glioblastoma invasion and extends survival by inhibiting Ca2+ release channel inositol 1,4,5-trisphosphate receptor (IP3R) subtype 3. Trifluoperazine (TFP) is an FDA-approved antipsychotic drug for schizophrenia. Interestingly, TFP has been recently reported to show a strong anticancer effect on lung cancer, hepatocellular carcinoma, and T-cell lymphoma. However, the possible anticancer effect of TFP on glioblastoma has not been tested. Here, we report that TFP potently suppresses proliferation, motility, and invasion of glioblastoma cells in vitro, and tumor growth in in vivo xenograft mouse model. Unlike caffeine, TFP triggers massive and irreversible release of Ca2+ from intracellular stores by IP3R subtype 1 and 2 by directly interacting at the TFP-binding site of a Ca2+-binding protein, calmodulin subtype 2 (CaM2). TFP binding to CaM2 causes a dissociation of CaM2 from IP3R and subsequent opening of IP3R. Compared with the control neural stem cells, various glioblastoma cell lines showed enhanced expression of CaM2 and thus enhanced sensitivity to TFP. On the basis of these findings, we propose TFP as a potential therapeutic drug for glioblastoma by aberrantly and irreversibly increasing Ca2+ in glioblastoma cells. Mol Cancer Ther; 16(1); 217-27. ©2016 AACR.

Ca(2+)-dependent regulation of the Ca(2+) concentration in the myometrium mitochondria. I. Trifluoperazine effects on mitochondria membranes polarization and [Ca(2+)](m).

Са2+-dependent regulation of Ca2+ exchange in mitochondria is carried out with participation of calmodulin. We have shown previously that calmodulin antagonists reduced the level of mitochondrial membrane polarization and induced increase of the ionized Са concentration in both the mitochondrial matrix and cell cytoplasm. The concentration-dependent influence of trifluoperazine on the level of polarization of mitochondrial membranes has been shown in this work. The coordinates of the Hill graphs were used to calculate the constant K0.5 and the Hill coefficient. K0.5 was 24.4 ± 5 μM (n = 10). The Hill coefficient was 2.0 ± 0.2, indicating the presence of two centers of the trifluoperazine binding. We have also studied [Ca2+]m changes, when incubating mitochondria in mediums of different composition: without ATP and ions of Mg (0-medium), in the presence of 3 mM Mg (Mg-medium) and 3 mM Mg + 3 mM ATP (Mg,ATP-medium). It was shown that the composition of the incubation medium affected the [Ca2+]m values in the absence of exogenous Ca2+ and did not affect them in the presence of the latter. Preincubation of mitochondria in mediums of different composition with 25 μM trifluoperazine did not affect the [Ca2+]m values both before and after the addition of 100 µМ Са2+ to the incubation medium. It was concluded, that trifluoperazine depolarized myometrial mitochondria membranes in concentration-dependent manner. However, mitochondria preincubation with 25 μM trifluope­razine accompanied by 50% decrease in membrane polarization did not affect the [Ca2+]m values.

Trifluoperazine regulation of calmodulin binding to Fas: a computational study.

Death-inducing signaling complex (DISC) formation is a critical step in Fas-mediated signaling for apoptosis. Previous experiments have demonstrated that the calmodulin (CaM) antagonist, trifluoperazine (TFP) regulates CaM-Fas binding and affects Fas-mediated DISC formation. In this study, we investigated the anti-cooperative characteristics of TFP binding to CaM and the effect of TFP on the CaM-Fas interaction from both structural and thermodynamic perspectives using combined molecular dynamics simulations and binding free energy analyses. We studied the interactions of different numbers of TFP molecules with CaM and explored the effects of the resulting conformational changes in CaM on CaM-Fas binding. Results from these analyses showed that the number of TFP molecules bound to CaM directly influenced α-helix formation and hydrogen bond occupancy within the α-helices of CaM, contributing to the conformational and motion changes in CaM. These changes affected CaM binding to Fas, resulting in secondary structural changes in Fas and conformational and motion changes of Fas in CaM-Fas complexes, potentially perturbing the recruitment of Fas-associated death domain for DISC formation. The computational results from this study reveal the structural and molecular mechanisms that underlie the role of the CaM antagonist, TFP, in regulation of CaM-Fas binding and Fas-mediated DISC formation in a concentration-dependent manner.

Phenothiazines inhibit S100A4 function by inducing protein oligomerization

S100A4, a member of the S100 family of Ca(2+)-binding proteins, regulates carcinoma cell motility via interactions with myosin-IIA. Numerous studies indicate that S100A4 is not simply a marker for metastatic disease, but rather has a direct role in metastatic progression. These observations suggest that S100A4 is an excellent target for therapeutic intervention. Using a unique biosensor-based assay, trifluoperazine (TFP) was identified as an inhibitor that disrupts the S100A4/myosin-IIA interaction. To examine the interaction of S100A4 with TFP, we determined the 2.3 A crystal structure of human Ca(2+)-S100A4 bound to TFP. Two TFP molecules bind within the hydrophobic target binding pocket of Ca(2+)-S100A4 with no significant conformational changes observed in the protein upon complex formation. NMR chemical shift perturbations are consistent with the crystal structure and demonstrate that TFP binds to the target binding cleft of S100A4 in solution. Remarkably, TFP binding results in the assembly of five Ca(2+)-S100A4/TFP dimers into a tightly packed pentameric ring. Within each pentamer most of the contacts between S100A4 dimers occurs through the TFP moieties. The Ca(2+)-S100A4/prochlorperazine (PCP) complex exhibits a similar pentameric assembly. Equilibrium sedimentation and cross-linking studies demonstrate the cooperative formation of a similarly sized S100A4/TFP oligomer in solution. Assays examining the ability of TFP to block S100A4-mediated disassembly of myosin-IIA filaments demonstrate that significant inhibition of S100A4 function occurs only at TFP concentrations that promote S100A4 oligomerization. Together these studies support a unique mode of inhibition in which phenothiazines disrupt the S100A4/myosin-IIA interaction by sequestering S100A4 via small molecule-induced oligomerization.

Abstract 96: Conformational and thermodynamics analyses of the regulation of trifluoperazine on camodulin binding to Fas: Implications for cancer chemotherapy

Abstract Fas-mediated signaling pathway is an important mechanism for apoptosis in a variety of cells, including cholangiocarcinoma and other cancer cells. The formation of death inducing signaling complex (DISC) is a critical step for Fas-mediated signaling. Recent experimental studies showed that calmodulin (CaM) binds to Fas and regulates Fas-mediated DISC formation and the binding of CaM to Fas is inhibited by the CaM antagonist, trifluoperazine (TFP) (J Cell Biochem, 103:788, 2008). The present study sought to determine the structural basis and molecular mechanisms of TFP regulation of Fas-mediated DISC formation. We used a combination of molecular dynamics simulations and binding free energy analyses to investigate the effect of TFP on CaM-Fas binding. We studied the interactions of different number(s) of TFP(s) with CaM and the effect of the resulting conformational changes of CaM on CaM/Fas binding. We found that the binding affinity of one TFP with CaM was affected by the sequential binding of other TFP(s) to CaM, which was consistent with near-UC circular dichroism data (Biochemistry 37:15300, 1998). The number of TFP(s) bound to CaM was shown to affect the conformational and motion changes of CaM, and thus directly affect CaM binding to Fas. Consistent with previous experimental observations that CaM-Fas binding was affected by TFP concentrations (J Biol Chem, 280:29964, 2005), we demonstrated that one TFP bound to CaM inhibited CaM-Fas binding while the subsequent two TFPs or four TFPs bound to CaM resulted in the recovery of CaM-Fas binding (Table 1). Results also showed that conformational and motional changes of Fas by binding to CaM were directly related to the number of TFPs bound to CaM, which could further affect Fas recruitment of FADD to the DISC. This study provides structural and thermodynamics evidence elucidating the role of the CaM antagonist, TFP, in regulating CaM-Fas binding and Fas-mediated DISC formation and apoptosis.Table 1.The change of CaM-Fas binding affinity by the CaM antagonist, TFP. CaM_Fas_WTCaM_1TFP_FasCaM_2TFPs_FasCaM_4TFPs_FasΔG−7.11±4.67−1.32±0.99−6.96±3.47−6.42±1.06ΔΔG 5.79*0.150.69All values in this table were expressed in terms of kcal/mol. ΔG is the binding free energy for the complex, and ΔΔG is the relative binding free energies with respect to the CaM-Fas complex without CaM antagonist TFP(s). * Differences are statistically significant (Student's t-test, p<0.05) Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 96.

Interaction of Antagonists with Calmodulin: Insights from Molecular Dynamics Simulations

We report results of 12 ns, all-atom molecular dynamics simulation (MDS) and Poisson-Boltzmann free energy calculations (PBFE) on calmodulin (CaM) bound to two molecules of trifluoperazine (TFP) and of N-(3,3, diphenylpropyl)- N'-[1- R-(3,4-bis-butoxyphenyl)-ethyl]-propylenediamine (DPD). X-ray data show very similar structures for the two complexes, yet the antagonists significantly differ with respect to their CaM binding affinities, the neutral DPD is much more potent. The goal of the study was to unravel the reason why TFP is less potent although its positive charge should facilitate binding. The electrostatic energy terms in CHARMM and binding free energy terms of the PBFE approach showed TFP a better antagonist, while inspection of hydrophobic contacts supports DPD binding. Detailed inspection of the amino acid contributions of PBFE calculations unravel that steric reasons oppose the favorable binding of TFP. Structural conditions are given for a successful drug design strategy, which may benefit also from charge-charge interactions.

Binding of trifluoperazine to apocalmodulin revealed by a combination of small-angle X-ray scattering and nuclear magnetic resonance

Small-angle X-ray scattering (SAXS) and nuclear magnetic resonance (NMR) studies were performed to investigate the binding of trifluoperazine (TFP) to Ca2+-free calmodulin (apoCaM) with N- and C-terminal globular domains connected by a linker. The SAXS and NMR measurements were taken throughout the titration of TFP. The SAXS analyses indicate that the binding of TFP induces structural changes from a dumbbell shape to a compact globular shape in solution. The formation of the complete globular structure requires 5.0 added equivalents of TFP. An analysis of NMR chemical-shift changes indicates that the C-terminal domain of apoCaM is involved in the binding of TFP. The SAXS and NMR data reflect the high structural flexibility of apoCaM.

Insights into the interactions between a drug and a membrane protein target by fluorine cross-polarization magic angle spinning NMR.

The fluorinated anti-psychotic drug trifluoperazine (TFP) has been shown to be a K(+)-competitive inhibitor of gastric H(+)/K(+)-ATPase, a membrane-embedded therapeutic target for peptic ulcer disease. This paper describes how variable contact time (19)F cross-polarization magic angle spinning (VCT-CP/MAS) NMR has been used to probe the inhibitory interactions between TFP and H(+)/K(+)-ATPase in native gastric membranes. The (19)F CP/MAS spectra for TFP in H(+)/K(+)-ATPase enriched (GI) gastric membranes and in control membranes containing less than 5 nmol of the protein indicated that the drug associates with the membranes independently of the presence of H(+)/K(+)-ATPase. The (19)F peak intensities in the VCT-CP/MAS experiment confirmed that TFP undergoes slow dissociation (k(off) < 100 s(-1)) from binding sites in GI membranes, and more rapid dissociation (k(off) < 100 s(-1)) from control membranes. The spectra showed that up to 40% of bound TFP was displaced from GI membranes by 100 mM K(+) and by the K(+)-competitive inhibitor TMPIP, but TFP was not displaced from the control membranes. Hence the spectra of TFP in GI membranes represent the drug bound to the K(+)-competitive inhibitory site of H(+)/K(+)-ATPase and to other non-specific sites. The affinity of TFP for the K(+)-competitive site (K(D) = 4 mM) was determined from a binding curve of (19)F peak intensity versus TFP concentration after correction for non-specific binding. The K(D) was much higher than the IC(50) for ATPase inhibition (8 microM), which suggests that the substantial non-specific binding of TFP to the membranes contributes to ATPase inhibition. This novel approach to probing ligand binding can be applied to a wide range of membrane-embedded pharmaceutical targets, such as G-protein coupled receptors and ion channels, regardless of the size of the protein or strength of binding.

Ca2+-bound calmodulin forms a compact globular structure on binding four trifluoperazine molecules in solution

Small-angle X-ray scattering (SAXS), which determines the radius of gyration, Rg, and the pair distance distribution function, was used to investigate the conformational changes of calmodulin (CaM) on binding to an antagonist, trifluoperazine (TFP), with or without Ca2+ in solution. We previously applied this SAXS method to CaM complexed with N-(6-aminohexyl)-5-chloro-1-naphthalenesulphonamide (W-7) [Osawa, Kuwamoto, Izumi, Yap, Ikura, Shibanuma, Yokokura, Hidaka and Matsushima (1999) FEBS Lett. 442, 173-177] and found that the binding of two W-7 TFP molecules to one Ca2+-saturated CaM molecule induces structural changes from a ‘dumb-bell’ shape to a compact globular shape. We report here that the most compact globular shape whose size is consistent with that of the 1:2 Ca2+-saturated CaM-W-7 complex is formed by the binding of four TFP molecules to one Ca2+-saturated CaM molecule. Even in the absence of Ca2+, the conformational changes of CaM occur on TFP binding, giving a slightly smaller Rg than Ca2+-free CaM alone.

Ca2+-bound calmodulin forms a compact globular structure on binding four trifluoperazine molecules in solution

Small-angle X-ray scattering (SAXS), which determines the radius of gyration, R(g), and the pair distance distribution function, was used to investigate the conformational changes of calmodulin (CaM) on binding to an antagonist, trifluoperazine (TFP), with or without Ca(2+) in solution. We previously applied this SAXS method to CaM complexed with N-(6-aminohexyl)-5-chloro-1-naphthalenesulphonamide (W-7) [Osawa, Kuwamoto, Izumi, Yap, Ikura, Shibanuma, Yokokura, Hidaka and Matsushima (1999) FEBS Lett. 442, 173-177] and found that the binding of two W-7 TFP molecules to one Ca(2+)-saturated CaM molecule induces structural changes from a 'dumb-bell' shape to a compact globular shape. We report here that the most compact globular shape whose size is consistent with that of the 1:2 Ca(2+)-saturated CaM-W-7 complex is formed by the binding of four TFP molecules to one Ca(2+)-saturated CaM molecule. Even in the absence of Ca(2+), the conformational changes of CaM occur on TFP binding, giving a slightly smaller R(g) than Ca(2+)-free CaM alone.

EPR and CD spectroscopy of fast myosin light chain conformation during binding of trifluoperazine.

The conformations of isolated rabbit fast myosin light chains (LCs) were modified using trifluoperazine (TFP), the hydrophobic calmodulin inhibitor. CD spectroscopy showed that TFP altered secondary structural content of the LCs, with half-maximal effects at TFP concentrations of approximately 14-50 microM, which is within the range required to alter muscle fiber contraction in both agonistic and antagonistic ways [Kurebayashi, N. & Ogawa, Y. (1988) J. Physiol. 403, 407-424]. EPR spectroscopy provided structural information from paramagnetic probes on C-terminal domain surfaces. In the absence of TFP, tauR (rotational correlation time) was 1.6 ns for both alkali light chains (ALCs) and 1.8 ns for light chain 2 (LC2). This was faster than expected for proteins of this size (approximately 10 ns). TFP progressively recruited the probes into populations with tauR sevenfold to 12-fold slower, with half-maximal effects at a TFP concentration of approximately 370-800 microM. The differences probably indicate that CD spectroscopy detects changes in protein conformation due to 'specific' TFP binding at the LC hydrophobic core, while less specific binding at higher TFP concentrations is required to effect conformational changes on the protein surfaces near the paramagnetic probes. TFP binding was generally not cooperative. Comparative sequence analysis between calmodulin, troponin C, and myosin LCs indicated considerable conservation between residues expected to bind TFP.

Molecular dynamics studies on the effect of trifluoperazine in the Ca 2+ binding process of calmodulin

A detailed investigation of the binding of trifluoperazine (TFP) to calmodulin (CAM) can give information on the loop-selectivity of the first Ca 2+ binding and determination of Ca 2+ cooperativity in the N-terminal domain. This information has been obtained by carrying out molecular dynamics simulations. By using interactive computer graphics, seven models for CAM are constructed according to sequential Ca 2+ occupancy and TFP occupancy. Analysis of the resulting structure shows that the binding site of the first Ca 2+ in the N-terminal domain is EFII rather than EFI. Electrostatic interactions between each Ca 2+ and its opposite loop play an important role in the cooperativity. TFP increases the Ca 2+ affinity and Ca 2+ cooperativity, and TFP prefers to bind to CAM with three rather than four bound Ca 2+ ions.

Trifluoperazine binding to mutant calmodulins

Trifluoperazine (TFP) binding by 14 calmodulins, including 12 produced by site-directed mutagenesis, was determined. While vertebrate calmodulin binds 4.2 +/- 0.2 equiv of TFP, Escherichia coli expressed but unmutated calmodulins bind about 5.0 +/- 0.5 equiv of TFP. The cause for this difference is not known. The E. coli expressed proteins consist of two different series expressed from different calmodulin genes, CaMI and SYNCAM. The wild-type genes code for proteins that differ by nine conservative amino acid substitutions. Both these calmodulins bind 5 equiv of TFP with similar affinities, thus none of these conservative substitutions has any additional effect on TFP binding. Some altered calmodulins (deletion of EE83-84 or SEEE81-84, changing DEE118-120----KKK, M124----I,E120----K, or E82----K) have no appreciable effect on TFP binding. Other mutations affect either the binding of one TFP (deletion of E84) or about two TFP (changing E84----K, EEE82-84----KKK, E67----A, DEQ6-8----KKK, or E11----K). The mutations that affect TFP binding are localized to three regions of calmodulin: The amino-terminal alpha-helix, the central helix between the two globular ends of calmodulin, and a calcium-binding site in the second calcium-binding domain. The results are consistent with each of these regions either directly participating in drug binding or involved structurally in maintaining or inducing the correct conformation for TFP binding in the amino-terminal half of calmodulin.

Trifluoperazine binding to porcine brain calmodulin and skeletal muscle troponin C

Binding of trifluoperazine (TFP), a phenothiazine tranquilizer, to porcine brain calmodulin (CaM) and rabbit skeletal muscle troponin C (Tn C) was measured by an automated high-performance liquid chromatography binding assay using a molecular sieving column; 10 micrograms of either protein per injection is sufficient for determining TFP binding, and results are comparable to those obtained by equilibrium dialysis. Very little binding was observed to either protein in the absence of Ca2+ while in the presence of Ca2+ both proteins bind 4 equiv of TFP. Other characteristics of TFP binding however are different for each protein. For CaM, half-maximal binding occurs at 5.8 microM TFP, the Hill coefficient is 0.82, and the fit of the data to the Scatchard equation is consistent with four independent TFP-binding sites. Binding of one melittin displaces two TFP from CaM. Thus, there are two recognizable classes of TFP-binding sites: those that are displaced by melittin and those that are not. TFP causes an increase in the Ca2+ affinity of CaM, and three Ca2+ must be bound to CaM for TFP binding to occur. The studies also yielded a measure of the intrinsic affinity of three of CaM's Ca2(+)-binding sites that is in agreement with previous reports. For troponin C, half-maximal binding occurs at 16 microM TFP, the Hill coefficient is 1.7, and the data best fit the Adair equation for four binding sites. The measured constants K1, K2, K3, and K4 were 2.5 X 10(4), 6.6 X 10(3), 5.8 X 10(5), and 2.0 X 10(5) M-1, respectively, in 1 mM Ca2+ and were similar when Mg2+ was additionally included. TFP also increases troponin C's Ca2+ affinity, and it is the low-affinity, Ca2(+)-specific binding sites that are affected. These studies yielded a measure of the intrinsic affinity of these Ca2(+)-binding sites that is in agreement with previous measurements.

Spectral studies of the Ca2+-dependent interaction of trifluoperazine with S100b.

S100b is a calcium-binding protein that will bind to many calmodulin target molecules in a Ca2+-dependent manner. In order to study the Ca2+-dependent binding properties of S100b, its interaction with a calmodulin antagonist, trifluoperazine (TFP), was investigated using [19F]- and [1H]-NMR and UV-difference spectroscopy. It was estimated from [19F]-NMR that in the absence of Ca2+, the k1/2 value of TFP was 130 microM, while its k1/2 value decreased to 28 microM in the presence of Ca2+. The addition of KCl was not antagonistic to the Ca2+-dependent interaction of TFP to S100b. The chemical exchange rate of TFP with Ca2+-bound S100b was estimated to be 9 x 10(2) sec-1. By comparison with TFP-calmodulin exchange rates, it is suggested that the TFP-binding site on S100b is structurally different from its binding sites on calmodulin. Proton NMR resonance broadening in the range 6.8-7.2 ppm, corresponding to phenylalanine nuclei of S100b, indicates that these residues may be involved in TFP binding. Addition of Ca2+ to a 1:1 mixture of S100b and TFP resulted in a red-shifted UV-difference spectrum, while no significant difference spectrum was detected when Mg2+ was added to a S100b-TFP solution. Thus, we suggest that Ca2+ induces the exposure of a hydrophobic domain on S100b containing one or more phenylalanine residues that will bind TFP but that this domain is different from the hydrophobic domain on calmodulin.

ChemInform Abstract: Interaction of Trifluoperazine with S100 Protein: A 19F NMR Study.

Abstract 19 F NMR spectra were measured to investigate the interaction of trifluoperazine (TFP) with porcine brain S100 protein (S100) under various conditions. It was found that TFP binds to S100 irrespective of Ca 2+ . However, in the presence of Ca 2+ the apparent affinity of TFP to protein ( K d = 20 μM) was greater than that in its absence ( K d = 85 μM). Zn 2+ also enhanced the binding of TFP to S100. The ratio of TFP bound to S100 was estimated to be nearly unity in the presence of Ca 2+ . It was also found that KCl only markedly affected the interaction of TFP with S100 in the presence of Ca 2+ . The 19 F NMR chemical shift of the TFP-S100 solution changed much depending upon the pH of the solution in the presence of Ca 2+ , while no remarkable pH dependence of the 19 F NMR chemical shift was observed for the TFP-S100 solution in the absence of Ca 2+ . These pH effects are in contrast wih those observed for the TFP-calmodulin solution.

Interaction of trifluoperazine with S100 protein: a 19F NMR study

19F NMR spectra were measured to investigate the interaction of trifluoperazine (TFP) with porcine brain S100 protein (S100) under various conditions. It was found that TFP binds to S100 irrespective of Ca 2+. However, in the presence of Ca 2+ the apparent affinity of TFP to protein ( K d = 20 μM) was greater than that in its absence ( K d = 85 μM). Zn 2+ also enhanced the binding of TFP to S100. The ratio of TFP bound to S100 was estimated to be nearly unity in the presence of Ca 2+. It was also found that KCl only markedly affected the interaction of TFP with S100 in the presence of Ca 2+. The 19F NMR chemical shift of the TFP-S100 solution changed much depending upon the pH of the solution in the presence of Ca 2+, while no remarkable pH dependence of the 19F NMR chemical shift was observed for the TFP-S100 solution in the absence of Ca 2+. These pH effects are in contrast wih those observed for the TFP-calmodulin solution.