The Dynamics of Subunit Rotation in a Eukaryotic Ribosome

Protein synthesis by the ribosome is coordinated by an intricate series of large-scale conformational rearrangements. Structural studies can provide information about long-lived states, however biological kinetics are controlled by the intervening free-energy barriers. While there has been progress describing the energy landscapes of bacterial ribosomes, very little is known about the energetics of large-scale rearrangements in eukaryotic systems. To address this topic, we constructed an all-atom model with simplified energetics and performed simulations of subunit rotation in the yeast ribosome. In these simulations, the small subunit (SSU; ∼1 MDa) undergoes spontaneous and reversible rotation events (∼8∘). By enabling the simulation of this rearrangement under equilibrium conditions, these calculations provide initial insights into the molecular factors that control dynamics in eukaryotic ribosomes. Through this, we are able to identify specific inter-subunit interactions that have a pronounced influence on the rate-limiting free-energy barrier. We also show that, as a result of changes in molecular flexibility, the thermodynamic balance between the rotated and unrotated states is temperature-dependent. This effect may be interpreted in terms of differential molecular flexibility within the rotated and unrotated states. Together, these calculations provide a foundation, upon which the field may begin to dissect the energetics of these complex molecular machines.

Sandwich phosphate complexes of macrocyclic tris(urea) ligands and their rotation around the anion

Sandwich-type phosphate complexes were formed by macrocyclic ligands incorporating both anion- (tris-urea unit) and cation-binding sites (polyether), which display a reversible rotation around the anion upon protonation/deprotonation of phosphate and binding of the cation (Emim+).

The Magnetization Reversal Processes Of Bulk (Nd, Y)-(Fe, Co)-B Alloy In The As-Quenched State

The magnetization reversal processes of bulk Fe64Co5Nd6Y6B19 alloy in the as-quenched state have been investigated. From the analysis of the initial magnetization curve and differential susceptibility versus an internal magnetic field it was deduced, that the main mechanism of magnetization reversal process is the pinning of domain walls at the grain’s boundaries of the Nd2Fe14B phase. Basing on the dependence of the reversible magnetization component as a function of magnetic field it was found that reversible rotation of a magnetic moment vector and motion of domain walls in multi-domain grains result in high initial values of the reversible component. The presence of at least two maxima on differential susceptibility of irreversible magnetization component in function of magnetic field imply existence of few pinning sites of domain walls in Fe64Co5Nd6Y6B19 alloy. The dominant interactions between particles have been determined on the basis of the Wohlfarth dependence. Such a behavior of Wohlfarth’s plot implies that the dominant interaction between grains becomes short range exchange interactions.

Enhancement of Reversible Rotation Journal Bearing Performance Using Elliptical Grooves

To improve the performance of a reversible rotation herringbone journal bearing (Rev-HGJB), this study uses reversible elliptical grooves on a journal bearing (Rev-EGJB) and numerically analyzes its characteristics, utilizing the spectral element method. Load capacity, pressure distribution, power loss, and dimensionless radial stiffness of the Rev-EGJB are compared with those of the Rev-HGJB. This comparison shows that the introduced Rev-EGJB exhibits a higher load capacity and a lower power loss than the Rev-HGJB. The pressure region in the Rev-EGJB is higher than that in the Rev-HGJB, which is achieved not only in the pressure-generated region, but also in the pressure-restored region. The load distributions of the Rev-HGJB and Rev-EGJB are also compared in order to determine how the elliptical grooves enhance the load characteristics. The optimum groove parameters of the Rev-EGJB at an eccentricity of 0.1 are investigated by studying the groove parametric matrix, which is given by taking several values in the effective range of each groove parameter. Ultimately, the radial stiffness of the Rev-EGJB with grooved bearing was also shown to be greater compared with that of a Rev-HGJB with optimum geometry; thus, the Rev-EGJB is more stable than the Rev-HGJB when the bearing is grooved.