Dynamics of water in the hydration layer of a partially unfolded structure of the protein HP-36

Elucidating the Sluggish Water Dynamics at the Ice-Binding Surface of the Hyperactive Tenebrio molitor Antifreeze Protein

Quasi-ice-like hydration waters on the ice-binding surface (IBS) of an antifreeze protein (AFP) commonly exhibit sluggish dynamics especially at low temperatures. In this work, we have analyzed molecular dynamics (MD) simulation trajectories at two different temperatures for Tenebrio molitor antifreeze protein (TmAFP) to explore whether the unique quasi-ice-like structuring of hydration water has any impact on making their dynamics slower on the IBS of the protein. Our calculation reveals that, as translational dynamics is coupled with the conformational fluctuations, hydration water on the IBS exhibits sluggish translational motion due to reduced flexibility of the IBS compared to that on the non-ice-binding surface (NIBS) of the protein. Interestingly, it is noticed that rotational motion of hydration water is not coupled with the conformational fluctuations of the surfaces. In that case, structural relaxations of the protein-water (PW) and water-water (WW) hydrogen bonds compete with each other to make the rotational dynamics of hydration water around the IBS either faster or slower with respect to those around the NIBS. At low temperature, the slower structural relaxation of water-water hydrogen bonds dominates and imparts sluggish rotational motion of the hydration water on the IBS of the protein. The slower structural relaxation of water-water hydrogen bonds and hence the retarded rotational dynamics, despite the weak short-lived PW hydrogen bonds on the IBS, is clearly a manifestation of the rigid quasi-ice-like structure of the hydration shell on that surface.

Microscopic dynamics of water around unfolded structures of barstar at room temperature

The breaking of the native structure of a protein and its influences on the dynamic response of the surrounding solvent is an important issue in protein folding. In this work, we have carried out atomistic molecular dynamics simulations to unfold the protein barstar at two different temperatures (400 K and 450 K). The two unfolded forms obtained at such high temperatures are further studied at room temperature to explore the effects of nonuniform unfolding of the protein secondary structures along two different pathways on the microscopic dynamical properties of the surface water molecules. It is demonstrated that though the structural transition of the protein in general results in less restricted water motions around its segments, but there are evidences of formation of new conformational motifs upon unfolding with increasingly confined environment around them, thereby resulting in further restricted water mobility in their hydration layers. Moreover, it is noticed that the effects of nonuniform unfolding of the protein segments on the relaxation times of the protein-water (PW) and the water-water (WW) hydrogen bonds are correlated with hindered hydration water motions. However, the kinetics of breaking and reformation of such hydrogen bonds are found to be influenced differently at the interface. It is observed that while the effects of unfolding on the PW hydrogen bond kinetics seem to be minimum, but the kinetics involving the WW hydrogen bonds around the protein segments exhibit noticeably heterogeneous characteristics. We believe that this is an important observation, which can provide valuable insights on the origin of heterogeneous influence of unfolding of a protein on the microscopic properties of its hydration water.

Long-Range Lipid-Water Interaction as Observed by ATR-FTIR Spectroscopy

It is commonly assumed that the structure of water at a lipid-water interface is influenced mostly in the first hydration layer. However, recent results from different experimental methods show that perturbation extends through several hydration layers. Due to its low light penetration depth, attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy is specifically suited to study interlamellar water structure in multibilayers. Results obtained by this technique confirm the long-range water structure disturbance. Consequently, in confined membrane environments nearly all water molecules can be perturbed. It is important to note that the behavior of confined water molecules differs significantly in samples prepared in excess water and in partially hydrated samples. We show in what manner the interlamellar water perturbation is influenced by the hydration level and how it is sequentially modified with a step-by-step dehydration of samples either by water evaporation or by osmotic pressure. Our results also indicate that besides different levels of hydration the lipid-water interaction is modulated by different lipid headgroups and different lipid phases as well. Therefore, modification of interlamellar water properties may clarify the role of water-mediated effects in biological processes.

Electronic polarization stabilizes tertiary structure prediction of HP-36

Molecular dynamic (MD) simulations with both implicit and explicit solvent models have been carried out to study the folding dynamics of HP-36 protein. Starting from the extended conformation, the secondary structure of all three helices in HP-36 was formed in about 50 ns and remained stable in the remaining simulation. However, the formation of the tertiary structure was difficult. Although some intermediates were close to the native structure, the overall conformation was not stable. Further analysis revealed that the large structure fluctuation of loop and hydrophobic core regions was devoted mostly to the instability of the structure during MD simulation. The backbone root-mean-square deviation (RMSD) of the loop and hydrophobic core regions showed strong correlation with the backbone RMSD of the whole protein. The free energy landscape indicated that the distribution of main chain torsions in loop and turn regions was far away from the native state. Starting from an intermediate structure extracted from the initial AMBER simulation, HP-36 was found to generally fold to the native state under the dynamically adjusted polarized protein-specific charge (DPPC) simulation, while the peptide did not fold into the native structure when AMBER force filed was used. The two best folded structures were extracted and taken into further simulations in water employing AMBER03 charge and DPPC for 25 ns. Result showed that introducing polarization effect into interacting potential could stabilize the near-native protein structure.

Dynamic properties of water around a protein-DNA complex from molecular dynamics simulations

Formation of protein-DNA complex is an important step in regulation of genes in living organisms. One important issue in this problem is the role played by water in mediating the protein-DNA interactions. In this work, we have carried out atomistic molecular dynamics simulations to explore the heterogeneous dynamics of water molecules present in different regions around a complex formed between the DNA binding domain of human TRF1 protein and a telomeric DNA. It is demonstrated that such heterogeneous water motions around the complex are correlated with the relaxation time scales of hydrogen bonds formed by those water molecules with the protein and DNA. The calculations reveal the existence of a fraction of extraordinarily restricted water molecules forming a highly rigid thin layer in between the binding motifs of the protein and DNA. It is further proved that higher rigidity of water layers around the complex originates from more frequent reformations of broken water-water hydrogen bonds. Importantly, it is found that the formation of the complex affects the transverse and longitudinal degrees of freedom of surrounding water molecules in a nonuniform manner.

Broadband depolarized light scattering study of diluted protein aqueous solutions

A broadband depolarized light scattering (DLS) study is performed on diluted lysozyme aqueous solutions as a function of temperature and concentration. The dynamical susceptibility, obtained in a wide spectral range (0.6-36000 GHz) through the coupled use of interferometric and dispersive devices, is interpreted and compared with neutron scattering and Raman-induced optical Kerr-effect literature data, thus giving a general picture of relaxation phenomena. We show that the proposed approach represents a suitable tool for investigating the hydration dynamics of protein-water solutions. A detailed analysis of the quasi-elastic scattering region evidences the existence of two distinct relaxational processes at picosecond time scales. The fast process (fractions of picosecond) is attributed to bulk water dynamics, while the slow one (few picoseconds) is attributed to dynamical rearrangements of water molecules strongly influenced by the protein (hydration water). The retardation effect here estimated of about 6-7 can be regarded as a direct measure of the increased protein-water and water-water hydrogen bond stability of the water molecules within the protein hydration shell. Interestingly, a similar effect was previously observed on small hydrophilic sugar molecules. Moreover, backbone and side chains torsional motions of the protein in the 600-5300 GHz frequency range are found to be insensitive to thermal variations and to eventual changes occurring in the premelting zone.

Hydration dynamics in a partially denatured ensemble of the globular protein human alpha-lactalbumin investigated with molecular dynamics simulations

Atomistic molecular dynamics simulations are used to probe changes in the nature and subnanosecond dynamical behavior of solvation waters that accompany partial denaturation of the globular protein, human alpha-lactalbumin. A simulated ensemble of subcompact conformers, similar to the molten globule state of human alpha-lactalbumin, demonstrates a marginal increase in the amount of surface solvation relative to the native state. This increase is accompanied by subtle but distinct enhancement in surface water dynamics, less favorable protein-water interactions, and a marginal decrease in the anomalous behavior of solvation water dynamics. The extent of solvent influx is not proportional to the increased surface area, and the partially denatured conformers are less uniformly solvated compared to their native counterpart. The observed solvation in partially denatured conformers is lesser in extent compared to earlier experimental estimates in molten globule states, and is consistent with more recent descriptions based on nuclear magnetic relaxation dispersion studies.