Left-handed Direction Research Articles

Torques within and outside the human spindle balance twist at anaphase.

At each cell division, nanometer-scale motors and microtubules give rise to the micron-scale spindle. Many mitotic motors step helically around microtubules in vitro, and most are predicted to twist the spindle in a left-handed direction. However, the human spindle exhibits only slight global twist, raising the question of how these molecular torques are balanced. Here, we find that anaphase spindles in the epithelial cell line MCF10A have a high baseline twist, and we identify factors that both increase and decrease this twist. The midzone motors KIF4A and MKLP1 are together required for left-handed twist at anaphase, and we show that KIF4A generates left-handed torque in vitro. The actin cytoskeleton also contributes to left-handed twist, but dynein and its cortical recruitment factor LGN counteract it. Together, our work demonstrates that force generators regulate twist in opposite directions from both within and outside the spindle, preventing strong spindle twist during chromosome segregation.

RNA and DNA flipons in health and disease

RNA and DNA flipons in health and disease Flipons are the next step in DNA research. What they are, their role in DNA and RNA coding, their impact on medical science, and their relation to the immune system are discussed here. Flipons are DNA and RNA sequences that adopt alternative forms inside our bodies. These different ways of folding nucleic acids were first discovered after Watson and Crick proposed their famous model for DNA called the ‘secret of life’. They were considered mere curiosities until the first crystal structure of DNA revealed that the DNA helix was wound in a left-handed direction rather than the expected right-handed twist of B-DNA.

Contraction Patterns of Post-Fontan Single Right Ventricle Versus Normal Left and Right Ventricles in Children: Insights From Principal Strain Analysis

Principal strain (PS) analysis quantifies three-dimensional myocardial deformation using three-dimensional speckle-tracking echocardiography. It defines both the amplitude and direction of the principal myocardial contraction, expressed as PS, and a perpendicular secondary strain of lower intensity. The aims of this study were to apply PS analysis to describe the contractile pattern in the single right ventricle (SRV) functioning as a systemic chamber in hypoplastic left heart syndrome, compared with the normal left ventricle (LV) and right ventricle (RV), and to compare SRV function using conventional echocardiographic evaluations. Fifty-four post-Fontan patients with hypoplastic left heart syndrome and age-matched control subjects (normal LV, n=64; normal RV, n=48) underwent computation of PS lines, ejection fraction (EF), end-diastolic volume indexed to body surface area, PS, secondary strain, circumferential strain, and longitudinal strain. The PS lines were compared between groups. Linear regressions with coefficient determination (R2) of strains, fractional area change, and tricuspid annular plane systolic excursion with EF and end-diastolic volume index were assessed in SRV. Additionally, the hypoplastic left heart syndrome cohort was equally divided into two groups with higher and lower EFs, followed by comparison of all parameters. The pattern of PS lines demonstrated a left-handed direction in the anterior free wall, a right-handed direction in the posterior free wall, and a circumferential direction in the medial wall in SRV. In contrast, in the normal LV, the principal contraction is in the circumferential direction, whereas in the normal RV, it is predominantly longitudinal. The R2 values for PS, secondary strain, and circumferential strain on EF were high (0.88, 0.72, and 0.90, respectively), whereas the R2 value for longitudinal strain was comparable with that for fractional area change (0.56 and 0.55). All parameters were independent of end-diastolic volume index. PS lines in the higher EF group showed a more circumferential orientation than in the lower EF group in SRV. PS analysis provides a unique functional map of SRV contraction. This map differs from corresponding maps of the normal LV and RV. This may be helpful in understanding the mechanisms of SRV function, although future longitudinal studies are needed.

A Novel Twist Sensor Based on Long-Period Fiber Grating Written in Side-Helical Polished Structure

We propose a novel method to write a long-period fiber grating in helical polished structure (HPLPFG) as a twist sensor. The helical structure is polished on one side of twisting fiber by CO2 laser following either right-hand or left-hand helix direction. The sensor can discriminate the twist direction and improve the twist sensitivity, due to its asymmetric and helical refractive index distribution. The twist and temperature characteristics of the sensor have been experimentally investigated. The twist sensitivities of the sensor (right-hand direction helix) are 0.199 nm/(rad/m) and 0.141 nm/(rad/m), and the twist sensitivities of the sensor (left-hand direction helix) are −0.119 nm/(rad/m) and −0.196 nm/(rad/m) in clockwise and anti-clockwise directions, respectively. The temperature sensitivities of the two sensors are 0.060 nm/°C and 0.063 nm/°C, respectively. The novel sensor has practical application potential in twist sensing.

Left or Right: How Does Amino Acid Chirality Affect the Handedness of Nanostructures Self-Assembled from Short Amphiphilic Peptides?

Peptide and protein fibrils have attracted an enormous amount of interests due to their relevance to many neurodegenerative diseases and their potential applications in nanotechnology. Although twisted fibrils are regarded as the key intermediate structures of thick fibrils or bundles of fibrils, the factors determining their twisting tendency and their handedness development from the molecular to the supramolecular level are still poorly understood. In this study, we have designed three pairs of enantiomeric short amphiphilic peptides: LI3LK and DI3DK, LI3DK and DI3LK, and LaI3LK and DaI3DK, and investigated the chirality of their self-assembled nanofibrils through the combined use of atomic force microscopy (AFM), circular dichroism (CD) spectroscopy, scanning electron microscopy (SEM), and molecular dynamic (MD) simulations. The results indicated that the twisted handedness of the supramolecular nanofibrils was dictated by the chirality of the hydrophilic Lys head at the C-terminal, while their characteristic CD signals were determined by the chirality of hydrophobic Ile residues. MD simulations delineated the handedness development from molecular chirality to supramolecular handedness by showing that the β-sheets formed by LI3LK, LaI3LK, and DI3LK exhibited a propensity to twist in a left-handed direction, while the ones of DI3DK, DaI3DK, and LI3DK in a right-handed twisting orientation.

Stereodynamics in reaction O(1D) + CH4 → OH + CH3

A theoretical study of the stereodynamics for reaction O(1D) + CH4 → OH + CH3 has been carried out using the quasiclassical trajectory method (QCT) on a potential energy surface structured by Gonzalez et al. The integral cross sections (ICSs), differential cross sections (DCSs) and product rotational angular momentum polarization have been calculated. With the collision energy increasing, the ICS decreases. There is no threshold energy, because no barrier is found on the minimum energy path. The DCS results show that the backward and forward scatterings exist at the same time. With the collision energy increasing, the dominant rotation of the product changes from the right-handed direction to the left-handed direction in planes parallel to the scattering plane. In the isotopic effect study, the decrease of the mass factor weakens the polarization degree of the rotational angular momentum vectors of the products.

Modeling of plasma processes in the slowly diverging magnetic fields at the exit of an applied-field magnetoplasmadynamic thruster

The performance of plasma thrusters with applied electric and magnetic fields can be enhanced by increasing the magnetic field strength, which is applied in the thrust chamber and the exit region propulsive plume. The ejected plasma which passes through a slowly diverging magnetic field will expand but can be restricted within the magnetic nozzle fields. To examine in detail the processes that occur, a new method with Particle-in-cell calculations is applied here. A two-dimensional axisymmetric particle dynamic code is used to model an AF-MPDT (Applied-field Magnetoplasmadynamic Thruster) for which extensive experimental data are available; it used Ar propellant and had applied magnetic coils of 101.5 mm radius and 153 mm length. From the results of the simulation study, it is found that total thrust increases linearly with magnetic field strength in the range of 0–0.1 T, but it decreases with increasing applied magnetic field up to 0.6 T. Thrust efficiency is found to increase to a maximum of 8.4% when B = 0.1 T; further, the peak value of nozzle efficiency reaches 91% at a moderate magnetic field (0.3 T). In detail, it is found that distributions of plasma density (1014–1015 m−3) that form in the magnetic nozzle demonstrate a significant pattern of concentration up to fields of B = 0.3 T where ions begin to be magnetized. However, azimuthal velocities of ions behave differently with different degrees of magnetization, i.e., weakly magnetized ions follow rotating electrons in a right-handed direction, while fully magnetized ions revolve in left-handed direction due to electromagnetic forces. Notably, a feedback effect on total magnetic field due to plasma motion identified in other studies is not found to be present in the working conditions of the AF-MPDT examined here.

Conical coils counter-current chromatography for preparative isolation and purification of tanshinones from Salvia miltiorrhiza Bunge

Modern counter-current chromatography (CCC) originated from the helical coil planet centrifuge. Recently, spiral coils were found to possess higher separation efficiency in both the retention of stationary phase and solutes resolution than other CCC coils like the helical and toroidal coils used on type-J CCC and cross-axis CCC. In this work, we built a novel conical coil CCC for the preparative isolation and purification of tanshinones from Salvia miltiorrhiza Bunge. The conical coils were wound on three identical upright tapered holders in head-to-tail and left-handed direction and connected in series. Compared with helical and spiral coil CCC, conical coil CCC not only placed CCC column in a two-dimensional centrifugal field, but also provided a potential centrifugal force gradient both in axial and radial directions. The extra centrifugal gradient made mobile phase move faster and enabled CCC much higher retention of stationary phase and better resolution. As a result, higher efficiency has been obtained with the solvent system of hexane–ethyl acetate–methanol–water (HEMWat) with the volume ratio of 5:5:7:3 by using conical coil CCC apparatus. Four tanshinones, including cryptotanshinone (1), tanshinone I (2), 1,2-dihydrotanshinquinone (3) and tanshinone IIA (4), were well resolved from 500mg to 1g crude samples with high purity. Furthermore, the conical coil CCC can make a much higher solid phase retention, which makes it to be a powerful separation tool with high throughput. This is the first report about conical coil CCC for separation of tanshinones and it may also be an important advancement for natural products isolation.

Mechanochemistry of a Viral DNA Packaging Motor

The pentameric ATPase motor gp16 packages double-stranded DNA into the bacteriophage ϕ29 virus capsid. On the basis of the results of single-molecule experimental studies, we propose a push and roll mechanism to explain how the packaging motor translocates the DNA in bursts of four 2.5 bp power strokes, while rotating the DNA. In this mechanism, each power stroke accompanies P i release after ATP hydrolysis. Since the high-resolution structure of the gp16 motor is not available, we borrowed characterized features from the P4 RNA packaging motor in bacteriophage ϕ12. For each power stroke, a lumenal lever from a single subunit is electrostatically steered to the DNA backbone. The lever then pushes sterically, orthogonal to the backbone axis, such that the right-handed DNA helix is translocated and rotated in a left-handed direction. The electrostatic association allows tight coupling between the lever and the DNA and prevents DNA from slipping back. The lever affinity for DNA decreases towards the end of the power stroke and the DNA rolls to the lever on the next subunit. Each power stroke facilitates ATP hydrolysis in the next catalytic site by inserting an Arg -finger into the site, as captured in ϕ12-P4. At the end of every four power strokes, ADP release happens slowly, so the cycle pauses constituting a dwell phase during which four ATPs are loaded into the catalytic sites. The next burst phase of four power strokes starts once spontaneous ATP hydrolysis takes place in the fifth site without insertion of an Arg finger. The push and roll model provides a new perspective on how a multimeric ATPase transports DNA, and it might apply to other ring motors as well.

MR study of the effect of infarct size and location on left ventricular functional and microstructural alterations in porcine models

To investigate the effect of infarct size and location on left ventricular (LV) functional and microstructural alterations in well-established porcine models. Myocardium infarction was induced in mini-pigs at apical septum (Group 1, n = 6) or basal lateral wall (Group 2, n = 6) by permanent occlusion of the left anterior descending or left circumflex coronary artery, respectively. In vivo cardiac magnetic resonance (CMR) was performed 4 and 13 weeks later. Hearts were then excised and examined by ex vivo diffusion tensor imaging (DTI) for myocardium structural changes in infarct, adjacent and remote regions. LV ejection fractions correlated negatively with infarct sizes. Between week 4 and 13, Group 1 exhibited more changes in end-systolic volume, LV mass, and ejection fraction, although it showed a smaller infarct volume percentage. Ex vivo results revealed the decreased water diffusion fractional anisotropy and increased diffusivities in infarct region in correlation with infarct size, but with no significant difference between the two groups. However, LV myocardial double-helical fiber architecture was found to alter in Group 1, shifting more towards left-handed direction as compared to controls. Postinfarct LV functional and structural remodeling is affected by both infarct size and location.

Angular Velocity Saturation in Planar Dust Cluster Rotation

Dust clusters, consisted of one up to twelve particles arranged in a horizontal plane, were formed in an inductively coupled rf plasma. When an axial magnetic field was applied to the dust clusters, the clusters rotate collectively in the left-handed direction with respect to the field. It was observed in our cluster rotation that, for single ring cluster, the angular velocity of the rotation increased linearly as the magnetic field strength increased. And for double ring dust clusters, the angular velocity increases linearly at low magnetic field and but then saturated at high magnetic field ~60 G). Comparison of our experimental results with theoretical models from literature has been made and an explanation for the angular velocity saturation of the dust cluster rotation has been provided.

Rotation of Coulomb Clusters in Magnetised Dusty Plasma

The rotation of Coulomb clusters with different numbers of micron-sized particles is studied experimentally in inductively coupled magnetised dusty plasma. When an external axial magnetic field was applied to dust Coulomb clusters, the clusters were observed to be rotating as a rigid body in the left-handed direction. We found the cluster rotation to be dependent on the particle number and configuration. Thus, the threshold magnetic field strength Bth at which the cluster would rotate decreased as the number of particles N increased and can be expressed by Bth = 200/N2. We also show that angular velocity ω depends on the magnetic field strength B as exp(–23/N)B8.3/N1.5.

Integrated structures of the linear plasmid SCP1 in two bidirectional donor strains of Streptomyces coelicolor A3(2)

The linear plasmid SCP1 is integrated into the central region of the chromosome of Streptomyces coelicolor A3(2). The integrated structures of SCP1 in two bidirectional donor strains, 2612 and A634, were analyzed by cloning and sequencing of the junctions between the SCP1 DNA and the chromosomal DNA. In the NF (normal fertility) strain 2612, SCP1 is integrated in a right-handed direction into ORF-X at the left end of the IS cluster in AseI fragment E. An almost intact left end of SCP1 is retained, while the right terminal inverted repeat (TIR-R) of SCP1 and a 33-kb chromosomal DNA segment including the IS cluster are deleted. In the NF-like strain A634, SCPI is also integrated into AseI fragment E in a left-handed direction. The left junction is composed of IS466 with complete deletion of TIR-R of SCP1, and the right junction is located at the left end of IS468A* with half of TIR-L being deleted. During the integration event, a 5.4-kb chromosomal DNA segment including IS468A, IS468B, IS469 and IS466A was duplicated so that this sequence is now present on both sides of SCP1. Since 2612 and A634 exhibit a similar bidirectional gradient of gene transfer, it is surprising that their chromosomal structures are so different.