Biomedical subjects

Nicolas Taulier

Publications and source records attributed to Nicolas Taulier.

12 recordsLinked to original sources

PubMed2006

Hydrophobic hydration in cyclodextrin complexation.

We report temperature-dependent acoustic and densimetric data on changes in volume, expansibility, and adiabatic compressibility accompanying the binding of 1-adamantanecarboxylic acid (AD) to beta-cyclodextrin (beta-CD). We interpret our volumetric results in terms of hydration. Based on our compressibility and expansibility data, we estimate that, at 25 degrees C, the binding of AD to beta-CD is accompanied by displacement of 20 to 25 water molecules from the hydration shells of the two interacting species. Comparison of the temperature-dependent compressibility changes accompanying the binding of AD to beta-CD with the compressibility contribution of aliphatic groups suggests that displaced water molecules predominantly come from the hydrophobic loci of AD and beta-CD. Thus, we conclude that hydrophobic interactions play a major role in stabilizing the AD-beta-CD complex. Our estimate of the number of water molecules released to the bulk is consistent with structural considerations. There is also good agreement between our volumetric data and osmotic stress results reported by Harries et al. (Harries, D.; Rau, D. C.; Parsegian, V. A. J. Am. Chem. Soc. 2005, 127, 2184). This observation is consistent with the picture in which the two techniques probe the same population of water molecules solvating AD and beta-CD.

Cyclodextrins↗

PubMed2006

A calmodulin-binding site on cyclin E mediates Ca2+-sensitive G1/s transitions in vascular smooth muscle cells.

Calcium transients are known to control several transition points in the eukaryotic cell cycle. For example, we have previously shown that a coordinate elevation in the intracellular free calcium ion concentration is required for G1- to S-phase cell cycle progression in vascular smooth muscle cells (VSMC). However, the molecular basis for this Ca2+ sensitivity was not known. Using buffers with differing [Ca2+], we found that the kinase activity of mouse and human cyclin E/CDK2, but not other G1/S-associated cell cycle complexes, was responsive to physiological changes in [Ca2+]. We next determined that this Ca2+-responsive kinase activity was dependent on a direct interaction between calmodulin (CaM), one of the major Ca2+-signal transducers of eukaryotic cells, and cyclin E. Pharmacological inhibition of CaM abrogated the Ca2+ sensitivity of cyclin E/CDK2 and retarded mouse VSMC proliferation by causing G1 arrest. We next defined the presence of a highly conserved 22 amino acid N-terminal CaM-binding motif in mammalian cyclin E genes (dissociation constant, 1.5+/-0.1 micromol/L) and showed its essential role in mediating Ca2+-sensitive kinase activity of cyclin E/CDK2. Mutant human cyclin E protein, lacking this CaM-binding motif, was incapable of binding CaM or responding to [Ca2+]. Taken together, these findings reveal CaM-dependent cyclin E/CDK2 activity as a mediator of the known Ca2+ sensitivity of the G1/S transition of VSMC.

Amino Acid Motifs↗

PubMed2006

Probing the transition state ensemble of a protein folding reaction by pressure-dependent NMR relaxation dispersion.

The F61A/A90G mutant of a redesigned form of apocytochrome b562 folds by an apparent two-state mechanism. We have used the pressure dependence of 15N NMR relaxation dispersion rate profiles to study the changes in volumetric parameters that accompany the folding reaction of this protein at 45 degrees C. The experiments were performed under conditions where the folding/unfolding equilibrium could be studied at each pressure without addition of denaturants. The exquisite sensitivity of the methodology to small changes in folding/unfolding rates facilitated the use of relatively low-pressure values (between 1 and 270 bar) so that pressure-induced changes to the unfolded state ensemble could be minimized. A volume change for unfolding of -81 mL/mol is measured (at 1 bar), a factor of 1.4 larger (in absolute value) than the volume difference between the transition state ensemble (TSE) and the unfolded state. Notably, the changes in the free energy difference between folded and unfolded states and in the activation free energy for folding were not linear with pressure. Thus, the difference in the isothermal compressibility upon unfolding (-0.11 mL mol(-1) bar(-1)) and, for the first time, the compressibility of the TSE relative to the unfolded state (0.15 mL mol(-1) bar(-1)) could be calculated. The results argue for a TSE that is collapsed but loosely packed relative to the folded state and significantly hydrated, suggesting that the release of water occurs after the rate-limiting step in protein folding. The notion of a collapsed and hydrated TSE is consistent with expectations based on earlier temperature-dependent folding studies, showing that the barrier to folding at 45 degrees C is entropic (Choy, W. Y.; Zhou, Z.; Bai, Y.; Kay, L. E. J. Am. Chem. Soc. 2005, 127, 5066-5072).

Cytochromes b↗

PubMed2006

Thermodynamics of interactions of water-soluble porphyrins with RNA duplexes.

We characterized the interactions of meso-tetrakis(4N-(2-hydroxyethyl)pyridinium-4-yl) porphyrin (TEtOHPyP4), meso-tetrakis(4N-allylpyridinium-4-yl) porphyrin (TAlPyP4), and meso-tetrakis(4N-metallylpyridinium-4-yl) porphyrin (TMetAlPyP4) with the poly(rA)poly(rU) and poly(rI)poly(rC) RNA duplexes between 18 and 45 degrees C by employing circular dichroism, light absorption, and fluorescence intensity spectroscopic measurements. Our results suggest that TEtOHPyP4 and TAlPyP4 intercalate into the poly(rA)poly(rU) and poly(rI)poly(rC) host duplexes, while TMetAlPyP4 associates with these RNA duplexes by forming outside-bound, self-stacked aggregates. We used our temperature-dependent absorption titration data to determine the binding constants and stoichiometry for each porphyrin-RNA binding event studied in this work. From the temperature dependences of the binding constants, we calculated the binding free energies, DeltaG(b), enthalpies, DeltaH(b), and entropies, DeltaS(b). For each RNA duplex, the binding enthalpy, DeltaH(b), is the most favorable for TEtOHPyP4 (an intercalator) followed by TAlPyP4 (an intercalator) and TMetAlPyP4 (an outside binder). On the other hand, for each duplex, external self-stacking of TMetAlPyP4 produces the most favorable change in entropy, DeltaS(b), followed by the intercalators TAlPyP4 and TEtOHPyP4. Thus, our results suggest that the thermodynamic profile of porphyrin-RNA binding may correlate with the binding mode. This correlation reflects the differential nature of molecular forces that stabilize/destabilize the two modes of binding-intercalation versus external self-stacking along the host duplex.

Kinetics↗

PubMed2006

Screening of lipid carriers and characterization of drug-polymer-lipid interactions for the rational design of polymer-lipid hybrid nanoparticles (PLN).

PURPOSE: The thermodynamics and solid state properties of components and their interactions in a formulation for polymer-lipid hybrid nanoparticles (PLN) were characterized for screening lead lipid carriers and rational design of PLN. METHODS: Verapamil HCI (VRP) was chosen as a model drug and dextran sulfate sodium (DS) as a counter-ionic polymer. Solubility parameters of VRP, VRP-DS complex, and various lipids were calculated and partition of VRP and VRP-DS in lipids was determined. Thermodynamics of VRP binding to DS was determined by isothermal titration calorimetry (ITC). The solid state properties of individual components and their interactions were characterized using differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD). RESULTS: Dodecanoic acid (DA) was identified as the best lipid carrier among all lipids tested based on the solubility parameters and partition coefficients. VRP-DS complexation was a thermodynamically favorable process. Maximum binding capacity of DS and the highest drug loading capacity of DA were obtained at an equal ionic molar ratio of DS to VRP. In the PLN formulation, DA remained its crystal structure but had a slightly lower melting point, while VRP-DS complex was in an amorphous form. CONCLUSIONS: Drug loading efficiency and capacity of a lipid matrix depend on the VRP-DS binding and the interactions of the complex with the lipid. A combined analysis of solubility parameters and partition coefficients is useful for screening lipid candidates for PLN preparation.

Calcium Channel Blockers↗

PubMed2005

Association of the minor groove binding drug Hoechst 33258 with d(CGCGAATTCGCG)2: volumetric, calorimetric, and spectroscopic characterizations.

We employed ultrasonic velocimetry, high-precision densimetry, circular dichroism and fluorescence spectroscopy, and isothermal titration calorimetry to characterize the binding of Hoechst 33258 to the d(CGCGAATTCGCG)(2) oligomeric duplex at 25 degrees C. We used this experimental combination to determine the full thermodynamic profile for the binding of Hoechst 33258 to the DNA. Specifically, we report changes in binding free energy, enthalpy, entropy, volume, and adiabatic compressibility accompanying the binding. We interpret our volumetric data in terms of hydration and evaluate the number of waters of hydration that become released to or taken up from the bulk. Our calorimetric data reveal that the drug-DNA binding event studied in this work is entropy-driven and proceeds with an unfavorable change in enthalpy. The favorable binding entropy predominantly results from hydration changes. In contrast to a large and positive change in hydrational entropy, the binding-induced change in configurational entropy is insignificant. The latter observation is consistent with the "lock-and-key" mode of minor groove binding.

Binding Sites↗

PubMed2005

Compressibility changes accompanying conformational transitions of apomyoglobin.

We used high-precision density and ultrasonic velocity measurements to characterize the native (N), molten globule (MG), and unfolded (U) conformations of apomyoglobin. The molten globule states that were studied in this work include the MG(pH4)(NaCl) state observed at pH 4 and 20 mM NaCl, the MG(pH4)(NaTCA) state observed at pH 4 and 20 mM sodium trichloracetate (NaTCA), the MG(pH2)(NaCl) state observed at pH 2 and 200 mM NaCl, and the MG(pH2)(NaTCA) state observed at pH 2 and 20 mM NaTCA. We used our densimetric and acoustic data to evaluate changes in adiabatic compressibility associated with the acid- or salt-induced N-to-MG, MG-to-U, MG-to-MG, and U-to-MG transitions of the protein. The N-to-MG(pH4)(NaCl) and N-to-MG(pH4)(NaTCA) transitions are accompanied by decreases in compressibility of -(3.0 +/- 0.6) x 10(-6) and -(2.0 +/- 0.6) x 10(-6) cm3 g(-1)bar(-1), respectively. The N-to-MG(pH2)(NaCl) and N-to-MG(pH2)(NaTCA) transitions are associated with compressibility changes of -(4.9 +/- 1.1) x 10(-6) and (0.7 +/- 0.9) x 10(-6) cm3 g(-1) bar(-1), respectively. We interpret these data in terms of the degree of unfolding of the various molten globule forms of apomyoglobin. In general, our compressibility data reveal significant disparities between the various equilibrium molten globule states of apomyoglobin while also quantitatively characterizing each of these states. Volumetric insights provided by our data facilitate gaining a better understanding of the folding pathways, intermediates, and kinetics of apomyoglobin folding.

Animals↗

PubMed2004

Energetics of nucleic acid stability: the effect of DeltaCP.

We report high-resolution differential scanning calorimetric data on the poly(dAdT)poly(dAdT), poly(dA)poly(dT), poly(dIdC)poly(dIdC), poly(dGdC)poly(dGdC), poly(rA)poly(rU), and poly(rI)poly(rC) nucleic acid duplexes. We use these data to evaluate the melting temperatures, TM, enthalpy changes, DeltaHM, and heat capacity changes, DeltaCP, accompanying helix-to-coil transitions of each polymeric duplex studied in this work at different NaCl concentrations. In agreement with previous reports, we have found that DeltaCP exhibits a positive, nonzero value, which, on average, equals 268 +/- 33 J mol(-1) K(-1). With DeltaCP, we have calculated the transition free energies, DeltaG, enthalpies, DeltaH, and entropies, DeltaS, for the duplexes as a function of temperature. Since, DeltaG, DeltaH, and DeltaS all strongly depend on temperature, the thermodynamic comparison between DNA and/or RNA duplexes (that may differ from one another with respect to sequence, composition, conformation, etc.) is physically meaningful only if extrapolated to a common temperature. We have performed such comparative analyses to derive differential thermodynamic parameters of formation of GC versus AT, AU, and IC base pairs as well as B' versus A and B helix conformations. We have proposed some general microscopic interpretations for the observed sequence-specific and conformation-specific thermodynamic differences between the duplexes.

Base Pairing↗

PubMed2004

On the stability of insulin delivered through a new glucose-responsive polymeric composite membrane.

A new glucose-responsive polymeric composite membrane that provided pulsatile insulin release was developed in our laboratory previously. To develop a clinically useful insulin delivery system, this study was designed to investigate factors influencing insulin stability during delivery by this membrane. The effects of stirring, release duration, insulin concentration and surfactant on insulin stability were studied under both incubation and delivery conditions in a buffer solution at 37 degrees C. The structural change of insulin was characterized by reverse-phase HPLC and circular dichroism. Hydrophobicity of various contact surfaces was determined by contact angle measurement. The results indicated that insulin concentration played an important role in the insulin stability, followed by stirring. Treating the membrane with a non-ionic surfactant prevented insulin denaturation during delivery through the membrane.

Acrylamides↗

PubMed2003

Volumetric effects of ionization of amino and carboxyl termini of alpha,omega-aminocarboxylic acids.

We have determined the partial molar volumes and adiabatic compressibilities of a homologous series of six alpha,omega-aminocarboxylic acids over a broad pH range at 25 degrees C. We interpret the resulting data in terms of the changes in hydration associated with neutralization of amino and carboxyl termini. By combining our volumetric results with pH-dependent data on 1-anilinonaphthalene-8-sulfonic acid fluorescence we propose the following explanation to the long-standing observation that changes in volume and compressibility accompanying neutralization of a carboxyl group depend on the type of the solute in contrast to solute-independent changes in these parameters accompanying neutralization of an amino group. Unlike amino groups, neutralized carboxyl groups are capable of forming hydrogen-bonded structures stabilized by hydrogen bonds between the carbonyl oxygen of one solute molecule and the hydroxyl group of another molecule. Formation of such hydrogen-bonded structures causes an additional decrease in solute hydration with concomitant increases in volume and compressibility. Furthermore, solutes with large aliphatic moieties may form larger associates stabilized, in addition to intermolecular hydrogen bonds, by hydrophobic interactions which will result in further increases in volume and compressibility. In the aggregate, our results emphasize the need for further studies focused on developing an understanding of the role of electrostatic interactions in stabilizing/destabilizing proteins and protein complexes.

Amino Acids, Diamino↗

PubMed2003

Volumetric characterization of homopolymeric amino acids.

We have determined the partial molar volumes, expansibilities, and adiabatic compressibilities for poly(L-alanine), poly(L-proline), and poly(L-threonine) within the temperature range of 18-55 degrees C. In addition, we have determined at 25 degrees C changes in volume, DeltaV, and adiabatic compressibility, DeltaK(S), associated with the coil-to-helix transitions of poly(L-lysine) and poly(L-glutamic acid) and the alpha-to-beta transition of poly(L-lysine). We have interpreted our volumetric data as suggesting that poly(L-alanine) and poly(L-proline) are not fully unfolded and, probably, retain some solvent-inaccessible core. Further, we propose that poly(L-threonine) is fully unfolded with the majority of its atomic groups being solvent-exposed. Near zero changes in volume and compressibility accompanying the coil-to-helix transitions of poly(L-lysine) and poly(L-glutamic acid) suggest that, in the absence of fortuitous compensations, the coil-to-helix transitions of the polypeptides do not result in any significant enhancement of solute hydration. By contrast, the alpha-to-beta transition of poly(L-lysine) causes slight but statistically significant increases in volume and compressibility, an observation that may suggest that the beta-sheet conformation of poly(L-lysine) is slightly less hydrated than its alpha-helical conformation. In general, our results provide a quantitative volumetric description of the hydration properties of the homopolymeric polypeptides investigated. Such characterizations should prove useful in developing an understanding of the role that solvent plays in the stabilization/destabilization of folded protein structures and protein complexes.

Circular Dichroism↗

PubMed2002

Compressibility of protein transitions.

We review the results of compressibility studies on proteins and low molecular weight compounds that model the hydration properties of these biopolymers. In particular, we present an analysis of compressibility changes accompanying conformational transitions of globular proteins. This analysis, in conjunction with experimental compressibility data on protein transitions, were used to define the changes in the hydration properties and intrinsic packing associated with native-to-molten globule, native-to-partially unfolded, and native-to-fully unfolded transitions of globular proteins. In addition, we discuss the molecular origins of predominantly positive changes in compressibility observed for pressure-induced denaturation transitions of globular proteins. Throughout this review, we emphasize the importance of compressibility data for characterizing protein transitions, while also describing how such data can be interpreted to gain insight into role that hydration and intrinsic packing play in modulating the stability of and recognition between proteins and other biologically important compounds.

Animals↗