Binding assessment of two arachidonic-based synthetic derivatives of adrenalin with ß-lactoglobulin: Molecular modeling and chemometrics approach.

A computational approach to predict the main binding modes of two adrenalin derivatives, arachidonoyl adrenalin (AA-AD) and arachidonoyl noradrenalin (AA-NOR) with the ß-lactoglubuline (BLG) as a nano-milk protein carrier is presented and assessed by comparison to the UV-Vis absorption spectroscopic data using chemometric analysis. Analysis of the spectral data matrices by using the multivariate curve resolution-alternating least squares (MCR-ALS) algorithm led to the pure concentration calculation and spectral profiles resolution of the chemical constituents and the apparent equilibrium constants computation. The negative values of entropy and enthalpy changes for both compound indicated the essential role of hydrogen bonding and van der Waals interactions as main driving forces in stabilizing protein-ligand complex. Computational studies predicted that both derivatives are situated in the calyx pose and remained in that pose during the whole time of simulation with no any significant protein structural changes which pointed that the BLG could be considered as a suitable carrier for these catecholamine compounds.

Computational mapping of the conformational transitions in agonist selective pathways of a G-protein coupled receptor.

The active state conformation of a G-protein coupled receptor (GPCR) is influenced by the chemical structure and the efficacy of the bound ligand. Insight into the active state conformation as well as the activation pathway for ligands with different efficacies is critical in designing functionally specific drugs for GPCRs. Starting from the crystal structure of the beta2-adrenergic receptor, we have used coarse grain computational methods to understand the modulation of the potential energy landscape of the receptor by two full agonists, two partial agonists, and an inverse agonist. Our coarse grain method involves a systematic conformational spanning of the receptor transmembrane helices followed by an energy minimization and ligand redocking in each sampled conformation. We have derived the activation pathways for several agonists and partial agonists, using a Monte Carlo algorithm, and these are in agreement with fluorescence spectroscopy measurements. The calculated pathways for the full agonists start with an energy downhill step leading to a stable intermediate followed by a barrier crossing leading to the active state. We find that the barrier crossing involves breaking of an interhelical hydrogen bond between helix5 and helix6, and polarization of the binding site residues by water facilitates the barrier crossing. The uphill step in the partial agonist salbutamol induced activation is distinct from full agonist norepinephrine, and originates from steric hindrance with the aromatic residues on helix6. Virtual ligand screening with the salbutamol-stabilized conformation shows enrichment of noncatechol agonists over the norepinephrine-stabilized conformation. Our computational method provides an unprecedented opportunity to derive hypotheses for experiments and also understand activation mechanisms in GPCRs.

The effect of solvation on biomolecular conformation: 2-amino-1-phenylethanol.

Small molecule neurotransmitters form one the most important classes of pharmaceutical molecules. While the behavior of these molecules in their neutral forms in the gas phase is well understood, their behavior in more biologically relevant scenarios (protonated and in aqueous solution) has received comparatively little attention. Here we address this problem by using molecular mechanics simulations to build up a detailed picture of the conformational behavior of 2-amino-1-phenylethanol, a noradrenaline analogue, in aqueous solution in both its neutral and protonated forms. For the sake of comparison, equivalent simulations are also performed on the gas-phase molecules and gas-phase hydrated clusters. These calculations reveal the important role that water has to play in determining the conformational preferences and dynamic behavior of the molecules. Water molecules are found to bridge between the various functional groups within the molecule, significantly affecting their relative stabilities in comparison to the gas-phase values. The reorganization of these solvation structures also provides a mechanism for conformational interconversion. The role of the solvent in mediating interactions between the various functional groups within the molecule suggests that in noradrenaline the catechol groups will be able to interact, albeit indirectly, with the other functional groups, thereby influencing the behavior of the molecule.

Quantum simulation of a hydrated noradrenaline analog with the torsional path integral method.

An extended version of the torsional path integral Monte Carlo (TPIMC) method is presented and shown to be useful for studying the conformation of flexible molecules in solvated clusters. The new technique is applied to the hydrated clusters of the 2-amino-1-phenyl-ethanol (APE) molecule. APE + nH2O clusters with n = 0-4 are studied at 100 and 300 K using both classical and quantum simulations. Only at the lower temperature is the hydration number n found to impact the conformational distribution of the APE molecule. This is shown to be a result of the temperature-dependent balance between the internal energy and entropy contributions to the relative conformer free energies. Furthermore, at 100 K, large quantum effects are observed in the calculated conformer populations. A particularly large quantum shift of 30% of the total population is calculated for the APE + 2H2O cluster, which is explained in terms of the relative zero point energy of the lowest-energy hydrated structures for this cluster. Finally, qualitative agreement is found between the reported calculations and recent spectroscopy experiments on the hydrated clusters of APE, including an entropically driven preference for the formation of AG-type hydrated structures and the formation of a water "droplet" in the APE + 4H2O cluster.

Theoretical conformational analysis for neurotransmitters in the gas phase and in aqueous solution. Norepinephrine.

The natural neurotransmitter (R)-norepinephrine takes the monocationic form in 93% abundance at the physiological tissue pH of 7.4. Ab initio and DFT/B3LYP calculations were performed for 12 protonated conformers of (R)-norepinephrine in the gas phase with geometry optimizations up to the MP2/6-311++G level, and with single-point calculations up to the QCISD(T) level at the HF/6-31G-optimized geometries. Four monohydrates were studied at the MP2/6-31G//HF/6-31G level. In the gas phase, the G1 conformer is the most stable with phenyl.NH(3)(+) gauche and HO(alc).NH(3)(+) gauche arrangements. A strained intramolecular hydrogen bond was found for conformers (G1 and T) with close NH(3)(+) and OH groups. Upon rotation of the NH(3)(+) group as a whole unit about the C(beta)-C(alpha) axis, a 3-fold potential was calculated with free energies for barriers of 3-12 kcal/mol at the HF/6-31G level. Only small deviations were found in MP2/6-311++G single-point calculations. A 2-fold potential was calculated for the phenyl rotation with free energies of 11-13 kcal/mol for the barriers at T = 310 K and p = 1 atm. A molecular mechanics docking study of (R)-norepinephrine in a model binding pocket of the beta-adrenergic receptor shows that the ligand takes a conformation close to the T(3) arrangement. The effect of aqueous solvation was considered by the free energy perturbation method implemented in Monte Carlo simulations. There are 4-5 strongly bound water molecules in hydrogen bonds to the conformers. Although hydration stabilizes mostly the G2 form with gauche phenyl.NH(3)(+) arrangement and a water-exposed NH(3)(+) group, the conformer population becomes T > G1 > G2, in agreement with the PMR spectroscopy measurements by Solmajer et al. (Z. Naturforsch. 1983, 38c, 758). Solvent effects reduce the free energies for barriers to 3-6 and 9-12 kcal/mol for rotations about the C(beta)-C(alpha) and the C(1)(ring)-C(beta) axes, respectively.