Caracterización energética de la unión de 1, 3, 6 - naftalén trisulfonato al factor de crecimiento para fibroblastos ácido humano: implicaciones para su uso como agente anti-angiogénico / Energetic characterization of 1, 3, 6 - naphtalene trisulfonate binding to human acidic fi broblast growth factor: implications for its anti-angiogenic use

Se ha estudiado, mediante calorimetría isotérmica de reacción, la interacción del agente anticancerígeno 1,3,6-naftalén trisulfonato con el factor de crecimiento para fi broblastos ácido humano. La afi nidad decrece con el aumento de la fuerza iónica. A pH 7,0 y NaCl 0,15 M, la constante de unión de la proteína con el ligando se encuentra en el rango 102 – 103 M-1, una afi nidad dos órdenes de magnitud menor que la del FGFa por heparina. El cambio de entalpía favorece la interacción, siendo el cambio de entropía desfavorable. De la dependencia del cambio de entalpía con la temperatura se calculó un pequeño cambio en la capacidad calorífi ca del proceso, con un valor excepcionalmente positivo de 90 cal K-1mol-1. A partir de los datos termodinámicos medidos y de ecuaciones paramétricas establecidas en la literatura, se calcularon cambios en la superfi cie accesible al disolvente, tanto polar como apolar, que acompañan a la interacción. Los resultados se compararon con los medidos mediante resonancia magnética nuclear. El estudio incluye consideraciones de bioenergética estructural sobre el posible uso de 1,3,6-naftalén trisulfonato como agente antiangiogénico o como molécula líder para el desarrollo de fármacos anti-angiogénicos

The equilibrium interaction of anti-cancer agent 1,3,6-naphatalene trisulfonate with human acidic fi broblast growth factor has been studied by calorimetry. The affi nity decreases with increasing ionic strength. At pH 7.0 and 0.15 M NaCl concentration, a binding constant of the protein with the ligand was estimated in the 102 – 103 M-1 range, an affi nity two orders of magnitude lower than that of aFGF with heparin. The interaction is enthalpically driven, and the entropy change is unfavorable. A small heat capacity change with an unusual positive value of 90 cal K-1mol-1 was determined from the temperature dependence of the enthalpies. Changes in accessible apolar and polar surface areas in the interaction were calculated from the thermodynamic data obtained and parametric equations in the literature. The results were compared with those measured from NMR data. The study includes structural bioenergetic considerations about the possible use of 1,3,6-naphatalene trisulfonate as an anti-angiogenic agent itself, or as a lead for the development of anti-angiogenic drugs

pH corrections and protein ionization in water/guanidinium chloride.

More than 30 years ago, Nozaki and Tanford reported that the pK values for several amino acids and simple substances in 6 M guanidinium chloride differed little from the corresponding values in low salt (Nozaki, Y., and C. Tanford. 1967. J. Am. Chem. Soc. 89:736-742). This puzzling and counter-intuitive result hinders attempts to understand and predict the proton uptake/release behavior of proteins in guanidinium chloride solutions, behavior which may determine whether the DeltaG(N-D) values obtained from guanidinium chloride-induced denaturation data can actually be interpreted as the Gibbs energy difference between the native and denatured states (Bolen, D. W., and M. Yang. 2000. Biochemistry. 39:15208-15216). We show in this work that the Nozaki-Tanford result can be traced back to the fact that glass-electrode pH meter readings in water/guanidinium chloride do not equal true pH values. We determine the correction factors required to convert pH meter readings in water/guanidinium chloride into true pH values and show that, when these corrections are applied, the effect of guanidinium chloride on the pK values of simple substances is found to be significant and similar to that of NaCl. The results reported here allow us to propose plausible guanidinium chloride concentration dependencies for the pK values of carboxylic acids in proteins and, on their basis, to reproduce qualitatively the proton uptake/release behavior for the native and denatured states of several proteins (ribonuclease A, alpha-chymotrypsin, staphylococcal nuclease) in guanidinium chloride solutions. Finally, the implications of the pH correction for the experimental characterization of protein folding energetics are briefly discussed.

Heat capacity analysis of oxidized Escherichia coli thioredoxin fragments (1--73, 74--108) and their noncovalent complex. Evidence for the burial of apolar surface in protein unfolded states.

We have calculated the absolute heat capacities of fragments 1--73 (N fragment) and 74--108 (C fragment) from thioredoxin, their complex and the uncleaved protein, from the concentration dependence of the apparent heat capacities of the solutions determined by differential scanning calorimetry. We find that, while the absolute heat capacities of uncleaved, unfolded thioredoxin and the C fragment are in good agreement with the theoretical values expected for fully solvated chains (calculated as the sum of the contributions of the constituent amino acids), the absolute heat capacities of the N fragment and the unfolded complex are about 2 kJ x K(-1) x mol(-1) lower than the fully solvated-chain values. We attribute this discrepancy to burial of the apolar surface in the N fragment (as burial of the polar area is expected to lead to an increase in heat capacity). Illustrative calculations suggest that burial of about 1000--1600 A(2) of apolar surface takes place in the N fragment (probably accompanied by the burial of a smaller amount of polar surface). In general, this work is supportive of heat capacity measurements on protein fragments being useful as probes of surface burial in studies to characterize protein unfolded states and the high regions of protein folding landscapes.

Native hydrogen bonds in a molten globule: the apoflavodoxin thermal intermediate.

The structure and energetics of protein-folding intermediates are poorly understood. We have identified, in the thermal unfolding of the apoflavodoxin from Anabaena PCC 7119, an equilibrium intermediate with spectroscopic properties of a molten globule and substantial enthalpy and heat capacity of unfolding. The structure of the intermediate is probed by mutagenesis (and phi analysis) of polar residues involved in surface-exposed hydrogen bonds connecting secondary-structure elements in the native protein. All hydrogen bonds analysed are formed in the molten globule intermediate, either with native strength or debilitated. This suggests the overall intermediate's topology and surface tertiary interactions are close to native, and indicates that hydrogen bonding may contribute significantly to shape the conformation and energetics of folding intermediates.