The Val34Met, Thr164Ile and Ser220Cys Polymorphisms of the β2-Adrenergic Receptor and Their Consequences on the Receptor Conformational Features: A Molecular Dynamics Simulation Study

The gene encoding the β2-adrenergic receptor (β2-AR) is polymorphic, which results in possible differences in a primary structure of this protein. It has been shown that certain types of polymorphisms are correlated with some clinical features of asthma, including airways reactivity, whereas the influence of other is not yet understood. Among polymorphisms affecting amino acids at positions 16, 27, 34, 164 and 220, the latter three are present in the crystal structure of β2-AR, which facilitates studying them by means of molecular dynamics simulations. The current study was focused on investigating to what extent the three polymorphisms of β2-AR (i.e., Val34Met, Thr164Ile and Ser220Cys) affect the interaction of β2-AR with its natural molecular environment which includes: lipid bilayer (in the case of all three polymorphs) and Gs protein (which participates in β2-AR-mediated signaling; in the case of Ser220Cys). We have designed and carried out a series of molecular dynamics simulations at different level of resolution (i.e., either coarse-grained or atomistic simulations), accompanied by thermodynamic integration protocol, in order to identify potential polymorphism-induced alterations in structural, conformational or energetic features of β2-AR. The results indicate the lack of significant differences in the case of energies involved in the β2-AR-lipid bilayer interactions. Some differences have been observed when considering the polymorphism-induced alterations in β2-AR-Gs protein binding, but their magnitude is also negligible in relation to the absolute free energy difference correlated with the β2-AR-Gs affinity. The Val34Met and Thr164Ile polymorphisms are weakly correlated with alteration of the conformational features of the receptor around polymorphic sites. On the contrary, it has been concluded that the Ser220Cys polymorphism is correlated with several structural alterations located in the intracellular region of β2-AR, which can induce G-protein binding and, subsequently, the polymorphism-correlated therapeutic responses. More precisely, these alterations involve vicinity of intracellular loops and, in part, are the direct consequence of disturbed interactions of Ser/Cys220 sidechain within 5th transmembrane domain. Structurally, the dynamic structure exhibited by the β2-ARSer220 polymorph is closer to the Gs-compatible structure of β2-AR

Exploring Free Energies of Specific Protein Conformations Using the Martini Force Field

Coarse-grained (CG) level molecular dynamics simulations are routinely used to study various biomolecular processes. The Martini force field is currently the most widely adopted parameter set for such simulations. The functional form of this and several other CG force fields enforces secondary protein structure support by employing a variety of harmonic potentials or restraints that favor the protein’s native conformation. We propose a straightforward method to calculate the energetic consequences of transitions between predefined conformational states in systems in which multiple factors can affect protein conformational equilibria. This method is designed for use within the Martini force field and involves imposing conformational transitions by linking a Martini-inherent elastic network to the coupling parameter λ. We demonstrate the applicability of our method using the example of five biomolecular systems that undergo experimentally characterized conformational transitions between well-defined structures (Staphylococcal nuclease, C-terminal segment of surfactant protein B, LAH4 peptide, and β2-adrenergic receptor) as well as between folded and unfolded states (GCN4 leucine zipper protein). The results show that the relative free energy changes associated with protein conformational transitions, which are affected by various factors, such as pH, mutations, solvent, and lipid membrane composition, are correctly reproduced. The proposed method may be a valuable tool for understanding how different conditions and modifications affect conformational equilibria in proteins

Ketamine Metabolites Enantioselectively Decrease Intracellular D-Serine Concentrations in PC-12 Cells.

D-Serine is an endogenous NMDA receptor co-agonist that activates synaptic NMDA receptors modulating neuronal networks in the cerebral cortex and plays a key role in long-term potentiation of synaptic transmission. D-serine is associated with NMDA receptor neurotoxicity and neurodegeneration and elevated D-serine concentrations have been associated with Alzheimer's and Parkinsons' diseases and amyotrophic lateral sclerosis. Previous studies have demonstrated that the ketamine metabolites (rac)-dehydronorketamine and (2S,6S)-hydroxynorketamine decrease intracellular D-serine concentrations in a concentration dependent manner in PC-12 cells. In the current study, PC-12 cells were incubated with a series of ketamine metabolites and the IC50 values associated with attenuated intracellular D-serine concentrations were determined. The results demonstrate that structural and stereochemical features of the studied compounds contribute to the magnitude of the inhibitory effect with (2S,6S)-hydroxynorketamine and (2R,6R)-hydroxynorketamine displaying the most potent inhibition with IC50 values of 0.18 ± 0.04 nM and 0.68 ± 0.09 nM. The data was utilized to construct a preliminary 3D-QSAR/pharmacophore model for use in the design of new and more efficient modulators of D-serine

Effect of (2R,6R)-hydroxynorketamine (HNK) on the levels of serine racemase protein in PC-12 cells.

<p>Cells were treated with various concentrations of HNK for 36 h and then total cell lysates were prepared for Western blot analysis. Top panel: representative immunoblot of monomeric serine racemase (m-SR; 36-kilodalton band). The blot was reprobed for β-actin, which was used as loading control. Bottom panel: relative levels of m-SR after quantification and normalization with β-actin. Bars represent the means ± SD of three independent experiments. * <i>P< 0</i>.<i>05</i> and ** <i>P< 0</i>.<i>01</i> as compared with control cells.</p

The concentration-dependent decrease of intracellular D-Ser concentrations produced by incubation of PC-12 cells with the enantiomers of ketamine (Ket) and its major metabolites expressed as IC₅₀ values and percent (%) maximum decrease from vehicle-treated PC-12 cells.

<p>The effect of the configuration at the chiral centers on the magnitude of the IC₅₀ value represented as the enantioselectivity factor α is derived by IC₅₀(2R isomer)/IC₅₀(2S isomer). The values for (<i>R</i>)-Ket were obtained from [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0149499#pone.0149499.ref017" target="_blank">17</a>] and ‘NA’ indicates that (<i>S</i>)-Ket increases intracellular D-Ser concentrations [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0149499#pone.0149499.ref017" target="_blank">17</a>]. Results are expressed as means ± SD, n = 3 independent experiments.</p