Stiffness of a new unilateral external fixator – a biomechanical study

Unilateral external fixator is commonly used to stabilize initial fractured bone for polytraumatised patients, which is simple and effective method. The stiffness property of the external fixator has a great influence on the local biomechanical environment of bone tissue. In order to investigate the rigidity characteristics of a novel fixator with serrated structure through comparing the stiffness of the Sarafix fixator and the novel fixator in experimental measurement. Polyacetal tubes simulating human tibia were fixed in novel fixator. Axial stiffness, torsional stiffness and bending stiffness of novel fixator were measured through universal material testing machine. In order to improve reliability, corresponding test must be repeated ten times. Due to the improvement of novel fixator’s structural, which has serrated connection between fixator joints, the performance of the novel fixator is better than Sarafix fixator under bending and torsional loads, there is no big difference in axial load for two fixators. The novel fixator has good stiffness properties, the novel fixator with serrated structure plays an important role to improve the stiffness of the novel fixator system. These analysis results can also aid the performance assessment of an novel external fixator and facilitate appropriate application of such a device

Resolving the genetic paradox of invasions: Preadapted genomes and postintroduction hybridization of bigheaded carps in the Mississippi River Basin

The genetic paradox of biological invasions is complex and multifaceted. In particular, the relative role of disparate propagule sources and genetic adaptation through postintroduction hybridization has remained largely unexplored. To add resolution to this paradox, we investigate the genetic architecture responsible for the invasion of two invasive Asian carp species, bighead carp (Hypophthalmichthys nobilis) and silver carp (H. molitrix) (bigheaded carps) that experience extensive hybridization in the Mississippi River Basin (MRB). We sequenced the genomes of bighead and silver carps (~1.08G bp and ~1.15G bp, respectively) and their hybrids collected from the MRB. We found moderate‐to‐high heterozygosity in bighead (0.0021) and silver (0.0036) carps, detected significantly higher dN/dS ratios of single‐copy orthologous genes in bigheaded carps versus 10 other species of fish, and identified genes in both species potentially associated with environmental adaptation and other invasion‐related traits. Additionally, we observed a high genomic similarity (96.3% in all syntenic blocks) between bighead and silver carps and over 90% embryonic viability in their experimentally induced hybrids. Our results suggest intrinsic genomic features of bigheaded carps, likely associated with life history traits that presumably evolved within their native ranges, might have facilitated their initial establishment of invasion, whereas ex-situ interspecific hybridization between the carps might have promoted their range expansion. This study reveals an alternative mechanism that could resolve one of the genetic paradoxes in biological invasions and provides invaluable genomic resources for applied research involving bigheaded carps

Structure and dynamics of N-terminal region of non-erythroid alpha spectrin revealed by SDSL-EPR methods.

Structure and dynamics of N-terminal region of non-erythroid alpha spectrin revealed by SDSL-EPR methods

The resting and activated conformations of the voltage sensor of Ci-VSP from functional and solvent accessibility determinations

The voltage sensor domain (VSD) is responsible for electromechanical transduction in voltage-gated ion channels and enzymes. In all known VSDs, both architecture and voltage-sensing mechanism are conserved: the positive charged residues (R/K) on the fourth transmembrane segment S4 respond to the voltage change across the membrane, which trigger its own conformation change leading to the response of downstream domain. A wealth of biophysical information on voltage sensors in the last two decades has revealed one of the major functional states - “up” or activated state. However, the structure and functional properties of the “down” or resting state remains controversial. Here, we show electrophysiological and structural studies of the voltage sensor from Ciona intestinalis voltage sensitive phosphatase (Ci-VSP), that point to conformational transitions between the resting and activated conformations of the sensor. The voltage dependence of Ci-VSP mutants, analyzed by gating charge measurement in oocytes, show significant shift in their Q-V relationships along the voltage axis (R217E −60 mV, R217Q −20 mV, WT +60 mV, D136N +130 mV). At 0 mV, these mutants populate different functional states under biochemical conditions: WT and D136N mostly in the “down” state while R217E is mostly in the “up” state. A Ci-VSD biochemical preparation was developed for each of the four mutants and studied by site-directed spin labeling EPR (SDSL-EPR) methods in proteoliposomes. Mobility and accessibility information revealed the secondary structure of transmembrane segments and their positions relative to membrane and each other, suggesting the extend and direction of the motion of S4 between “up” and “down” states. These results are consistent with the down movement of S4 under hyperpolarization and render critical structural information, that allow us to propose a gating mechanism for Ci-VSD

The Resting and Activated Conformations of the Voltage Sensor of Ci-VSP from Functional and Solvent Accessibility Determinations

The voltage sensor domain (VSD) is responsible for electromechanical transduction in voltage-gated ion channels and enzymes. In all known VSDs, both architecture and voltage-sensing mechanism are conserved: the positive charged residues (R/K) on the fourth transmembrane segment S4 respond to the voltage change across the membrane, which trigger its own conformation change leading to the response of downstream domain. A wealth of biophysical information on voltage sensors in the last two decades has revealed one of the major functional states - “up” or activated state. However, the structure and functional properties of the “down” or resting state remains controversial. Here, we show electrophysiological and structural studies of the voltage sensor from Ciona intestinalis voltage sensitive phosphatase (Ci-VSP), that point to conformational transitions between the resting and activated conformations of the sensor. The voltage dependence of Ci-VSP mutants, analyzed by gating charge measurement in oocytes, show significant shift in their Q-V relationships along the voltage axis (R217E −60 mV, R217Q −20 mV, WT +60 mV, D136N +130 mV). At 0 mV, these mutants populate different functional states under biochemical conditions: WT and D136N mostly in the “down” state while R217E is mostly in the “up” state. A Ci-VSD biochemical preparation was developed for each of the four mutants and studied by site-directed spin labeling EPR (SDSL-EPR) methods in proteoliposomes. Mobility and accessibility information revealed the secondary structure of transmembrane segments and their positions relative to membrane and each other, suggesting the extend and direction of the motion of S4 between “up” and “down” states. These results are consistent with the down movement of S4 under hyperpolarization and render critical structural information, that allow us to propose a gating mechanism for Ci-VSD

Structural dynamics in the resting and activated states of the voltage sensor of Ci-VSP from dipolar distance measurements

The mechanism of electromechanical transduction in voltage sensing domains remains controversial. Here, we have probed the conformation of the voltage sensor of Ci-VSP in different functional states by means of EPR-based distance measurements. Ci-VSP is a voltage-sensing phosphatase from Ciona intestinalis. Although it is coupled to a cytoplasmic phosphatase, its voltage-sensing domain (VSD) is homologous to voltage sensors found in voltage-gated ion channels. It therefore serves as an excellent model to study voltage sensor movement independent of the interaction with pore domain. On the basis of voltage dependence of Ci-VSP sensing currents (Q-V curves), it is agreed that, at 0 mV, the S4 of wild-type Ci-VSP is in the resting conformation (down state). The arginine at position 217, located in the extracellular end of S4, has a strong effect on the voltage dependence of Ci-VSP sensing currents. Mutations at arginine 217 with a neutral or negative residue (R217Q or R217E), lead to a large leftward shifts in the Q-V curve so that, at 0 mV, the sensor is in the activated conformation (up state). This provides a unique opportunity to monitor the conformational differences in the VSD between resting and activated states in the absence of membrane potential. We expressed and purified a series of double cysteine mutants in the isolated voltage sensor (S1 to S4) of Ci-VSP in wild-type and R217E backgrounds, and measured distances using CW-based dipolar broadenings (for short distances, 8 to 20 Å) and double electron-electron resonance (DEER) spectroscopy (for longer distances, 20 to 50 Å). Our preliminary analysis of the distance measurements suggest defined conformational differences between resting and activated states of the VSD